Chapter 1 Introduction to Java Chapter 1. 2 History of Java Java – Originally for _______________ consumer- electronic devices – Then used for creating

Chapter 1

Introduction to Java

Chapter 1

2

History of Java

• Java– Originally for _______________ consumer-

electronic devices

– Then used for creating Web pages with _______________

– Now also used to:• Develop large-scale enterprise applications

• Enhance WWW ___________ functionality

• Provide applications for consumer devices (cell phones, etc.)

3

Java Class Libraries

• Classes– Include methods that ________________

• Return information after task completion

– Used to build Java programs

• Java provides class ________________– Known as Java APIs

(A_______________ P________________ I ________________

4

FORTRAN, COBOL, Pascal and Ada

• ___________________– FORmula TRANslator

• COBOL– COmmon ______________ Oriented Language

• Pascal– ______________ programming

• Ada– Multitasking

5

BASIC, Visual Basic, Visual C++, C# and .NET

• BASIC– Beginner’s All-Purpose ___________ ________ Code

• .NET– .NET platform

• Visual Basic .NET– Based on BASIC

• _______________ C++– Based on C++

• C#– Based on C++ and ___________________

6

Typical Java Development Environment

• Java programs normally undergo five phases– Edit

• Programmer __________ program (and stores program on disk)

– Compile• Compiler creates bytecodes from program

– __________________• Class loader stores bytecodes in memory

– Verify• _______________ Verifier confirms bytecodes do not violate

security restrictions

– Execute• JVM translates bytecodes into machine language

7

Fig. 1.1 Typical Java development environment.

8

Creating a Program with JCreator

• Click on the JCreator ____________

• IDE windowappears

9


• Click on File, New, then P______________

• Project Wizard appears– Choose Java ________________ template

10


• Give the project a _________________

• Then click Next

11


• You will want the JDK version 1.5

At this point you can click on FinishAt this point you can click on Finish

12


• Now we create our class (the program) with File, New, and Class

13


• The wizard creates a __________________.

• Now complete the program with the required commands.

14


• Run the compiler with Build, and CompileFile

___________________ shows in bottom pane. This is where compiler error messages will be displayed.

15


• To run the compiled program click on Build, and _________________

• Program runs in separate window

16

Chapter 2

Introductionto Java Applications

17

2.1 Introduction

• Java application programming– Display ___________________________

– Obtain information from the user

– ____________________ calculations

– Decision-making fundamentals

18

2.2 First Program in Java: Printing a Line of Text

• Application– Executes when you use the java command to

launch the J_______V_______ M________Sample program

– Displays a line of text

– Illustrates several important Java language features

19

2.2 First Program in Java: Printing a Line of Text (Cont.)

– Comments start with: ____________• Comments ignored during program execution• Document and describe code• Provides code readability

– Traditional comments: ________________/* This is a traditional comment. It can be split over many lines */

– Another line of comments– Note: line numbers not part of program, added for

reference

1 // Fig. 2.1: Welcome1.java

2 // Text-printing program.

20


– Blank line• Makes program more __________________• Blank lines, spaces, and tabs are white-space characters

– _______________________ by compiler

– Begins class declaration for class Welcome1• Every Java program has at least one ________________• Keyword: words reserved for use by Java

– class keyword followed by class name• Naming classes: ______________________________

– SampleClassName

3

4 public class Welcome1

21


– Java identifier• Series of characters consisting of letters, digits,

underscores ( _ ) and dollar signs ( $ )• Does not begin with a ____________, has no _______• Examples: Welcome1, $value, _value, button7

– 7button is invalid• Java is case sensitive (capitalization matters)

– a1 and A1 are different

– In chapters 2 to 7, use public class• Certain details not important now • Mimic certain features, discussions later


22


– Saving files• File name must be class name with ._______ extension

• Welcome1.java

– Left brace {• Begins _________________ of every class

• Right brace ends declarations (line 13)


5 {

23


– Part of every Java application• Applications begin executing at main

– Parentheses indicate main is a ______________ (Ch. 3 and 6)– Java applications contain one or more methods

• Exactly one method must be called _________________

– Methods can perform tasks and return information• ______________ means main returns no information• For now, mimic main's first line

– Left brace begins body of method declaration• Ended by right brace } (line 11)

7 public static void main( String args[] )

8 {

24


– Instructs computer to perform an action• Prints string of characters

– String - series characters inside ___________ quotes• White-spaces __________ are not ignored by compiler

– System.out• Standard output object• Print to command window (i.e., MS-DOS prompt)

– Method System.out.println • Displays line of text

– This line known as a statement• Statements must end with __________________

9 System.out.println( "Welcome to Java Programming!" );

25


– Ends method declaration

– Ends class declaration

– Can add __________________ to keep track of ending braces

11 } // end method main

13 } // end class Welcome1

26

2.3 Modifying Our First Java Program

• Modifying programs– Welcome2.java (Fig. 2.3) produces same output as Welcome1.java (Fig. 2.1)

– Using different code

– Line 9 displays “Welcome to ” with cursor remaining on printed line

– Line 10 displays “Java Programming! ” _____________ with cursor on next line

9 System.out.print( "Welcome to " ); 10 System.out.println( "Java Programming!" );

27

2.3 Modifying Our First Java Program (Cont.)

• Escape characters– Backslash ( \ )

– Indicates _____________________ be output

• ____________________ characters (\n)– Interpreted as “special characters” by methods System.out.print and System.out.println

– Indicates cursor should be at the beginning of the next line

– Welcome3.java (Fig. 2.4)

– Line breaks at \n9 System.out.println( "Welcome\nto\nJava\nProgramming!" );

28

Fig. 2.5 | Some common escape sequences.

29

2.4 Displaying Text with printf

•System.out.printf– New feature of J2SE 5.0

– Displays _________________ data

– Format string• Fixed text

• Format ____________ – placeholder for a value

– Format specifier %s – placeholder for a _______

– Other format specifiers

9 System.out.printf( "%s\n%s\n", 10 "Welcome to", "Java Programming!" );

30

Formatting Output with printf

•printf– Precise output formatting

• Conversion specifications: flags, field widths, precisions, etc.

– Can perform • _________________________• aligning columns• right/left _______________________• inserting literal characters• exponential format• octal and hexadecimal format• fixed width and ____________________• date and time format

31

Formatting Output with printf (Cont.)

• Format String– Describe the output format

– Consist of fixed text and format specifier

• Format specifier– Placeholder for a value

– Specify the ________________ of data to output

– Begins with a ________________ and is followed by a conversion character

• E.g., %s, %d

– Optional formatting information• Argument index, flags, field width, precision

• Specified between % and conversion character

32

Printing Integers

• Integer– Whole number (no decimal point): 25, 0, -9– Positive, negative, or zero– Only __________________ prints by default (later we shall

change this)

• Format– printf( format-string, argument-list );– format-string

• Describe the output format

– argument-list• Contain the ____________ corresponding to each format

specifier

33

Integer conversion characters.

• View demonstration program Fig. 28.3– Note output of positive, negative numbers

– Note octal (base 8) and hexadecimal (base 16) options

34

Printing Floating-Point Numbers

• Floating Point Numbers– Have a ______________ point (33.5)

– Computerized scientific notation (exponential notation)• 150.4582 is 1.504582 x 10² in scientific

• 150.4582 is 1.504582e+02 in exponential (e stands for exponent)

• use e or E

– f – print _________________ with at least one digit to left of decimal

– g (or G) - prints in f or e (E) • Use exponential if the magnitude is less than 10-3, or

greater than or equal to 107

35

Floating-point conversion characters.

• View program using printf for floating point numbers, Figure 28.4

Conversion character Description

e or E Display a floating-point value in exponential notation. When conversion character E is used, the output is displayed in uppercase letters.

F Display a floating-point value in decimal format.

g or G Display a floating-point value in either the floating-point format f or the exponential format e based on the magnitude of the value. If the magnitude is less than 10–3, or greater than or equal to 107, the floating-point value is printed with e (or E). Otherwise, the value is printed in format f. When conversion character G is used, the output is displayed in uppercase letters.

a or A Display a floating-point number in hexadecimal format. When conversion character A is used, the output is displayed in uppercase letters.

Conversion character Description

e or E Display a floating-point value in exponential notation. When conversion character E is used, the output is displayed in uppercase letters.

F Display a floating-point value in decimal format.

g or G Display a floating-point value in either the floating-point format f or the exponential format e based on the magnitude of the value. If the magnitude is less than 10–3, or greater than or equal to 107, the floating-point value is printed with e (or E). Otherwise, the value is printed in format f. When conversion character G is used, the output is displayed in uppercase letters.

a or A Display a floating-point number in hexadecimal format. When conversion character A is used, the output is displayed in uppercase letters.

36

Printing Strings and Characters

• Conversion character c and C– Require ________________

– C displays the output in uppercase letters

• Conversion character s and S– String

– Object• Implicitly use object’s _______________ method

– S displays the output in uppercase letters

• View program demonstrating character conversion with printf, Fig. 28.5

37

Printing with Field Widths and Precisions

• Field width– Size of field in which data is printed

– If width larger than data, default __________ justified• If field width too small, ______________ to fit data

• Minus sign uses one character position in field

– Integer width inserted between % and conversion specifier• E.g., %4d – field width of 4

– Can be used with all format specifiers except the _________ separator (%n)

• View program demonstrating field width, Fig. 28.12

38


• Precision– Meaning varies depending on data type– Floating point

• Number of digits to appear ____________ decimal (e or E and f)

• Maximum number of significant digits (g or G)

– Strings• ____________ number of characters to be written from string

– Format• Use a dot (.) then precision number after %

e.g., %.3f

• View program demonstrating precision, Fig. 28.13

39


• Field width and precision– Can both be specified

• %width.precision

%5.3f

– ________________ field width – left justified

– Positive field width – right justified

– Precision must be _________________• Example:

printf( "%9.3f", 123.456789 );

40

2.5 Another Java Application: Adding Integers

• Program Fig. 2.7 to do keyboard input– Use ___________ to read two integers from user

– Use printf to display sum of the two values

– Use packages

41

2.5 Another Java Application: Adding Integers (Cont.)

– import declarations • Used by _________________ to identify and locate classes used

in Java programs

• Tells compiler to load class Scanner from java.util package

– Begins public class Addition• Recall that file name must be Addition.____________

– Lines 8-9: begins main

3 import java.util.Scanner; // program uses class Scanner

5 public class Addition 6 {

42


– Variable Declaration Statement– Variables

• Location in memory that stores a _____________– Declare with name and type before use

• Input is of type Scanner – Enables a program to read data for use

• Variable name: any valid identifier

– Declarations end with semicolons ;– Initialize variable in its ________________

• Equal sign• Standard input object

– System.in

10 // create Scanner to obtain input from command window11 Scanner input = new Scanner( System.in );

43


– Declare variable number1, number2 and sum of type int• int holds integer values (whole numbers): i.e., 0, -4, 97

• Types ___________ and double can hold decimal numbers

• Type char can hold a __________ character: i.e., x, $, \n, 7

• int, float, double and char are _____________ types

– Can add comments to describe purpose of variables

– Can declare ______________ variables of the same type in one declaration

– Use comma-separated list

13 int number1; // first number to add14 int number2; // second number to add15 int sum; // second number to add

int number1, // first number to add number2, // second number to add sum; // second number to add

44


– Message called a ____________ - directs user to perform an action

– Package java.lang

– Result of call to nextInt given to number1 using assignment operator =

• Assignment statement• = binary operator - takes ____________ operands

– Expression on right evaluated and assigned to variable on left

• Read as: number1 __________________ input.nextInt()

17 System.out.print( "Enter first integer: " ); // prompt

18 number1 = input.nextInt(); // read first number from user

45


– Similar to previous statement• Prompts the user to input the second integer

– Similar to previous statement• Assign variable number2 to second integer input

– Assignment statement• ___________ of number1 and number2 (right hand side)• Uses assignment operator = to assign result to variable sum• Read as: sum gets the value of number1 + number2• number1 and number2 are _________________

20 System.out.print( "Enter second integer: " ); // prompt

21 number2 = input.nextInt(); // read second number from user

23 sum = number1 + number2; // add numbers

46


– Use System.out.printf to display results

– _______________ specifier %d• Placeholder for an int value

– Calculations can also be performed inside _______________

– Parentheses around the expression number1 + number2 are not required

25 System.out.printf( "Sum is %d\n: " , sum ); // display sum

System.out.printf( "Sum is %d\n: " , ( number1 + number2 ) );

47

2.6 Memory Concepts

• Variables

– Every variable has a name, a ___________, a _______________ and a value

• Name corresponds to location in memory

– When new value is placed into a variable, replaces (and ______________) previous value

– ________________ variables from memory does not change them

48

2.7 Arithmetic

• Arithmetic calculations used in most programs

– Usage • * for multiplication

• / for division

• % for ___________________

• +, -

– Integer division _____________ remainder7 / 5 evaluates to 1

– Remainder operator % returns the remainder 7 % 5 evaluates to 2

49

Fig. 2.11 | Arithmetic operators.

50

2.7 Arithmetic (Cont.)

• Operator precedence – Some arithmetic operators act before others (i.e.,

multiplication before addition)• Use ___________________ when needed

– Example: Find the average of three variables a, b and c

• Do not use: a + b + c / 3

• Use: ( a + b + c ) / 3

51

Fig. 2.12 | Precedence of arithmetic operators.

Operator(s) Operation(s) Order of evaluation (precedence)

*

/

%

Multiplication

Division

Remainder

Evaluated first. If there are several operators of this type, they are evaluated from left to right.

+

-

Addition

Subtraction

Evaluated next. If there are several operators of this type, they are evaluated from left to right.

52

Operator Precedence Chart

Hierarchy of Java operators with the highest precedence shown first.• Expressions inside parentheses are evaluated first; nested parentheses are evaluated from the innermost parentheses to the outer. • Operators in the same row in the chart have equal precedence.

Operator Type Order of Evaluation

( ) [ ] .

ParenthesesArray subscriptMember access

left to right

++ -- Prefix increment, decrement

right to left

++ -- - Postfix increment, decrementUnary minus

right to left

* / % Multiplicative left to right

+ - Additive left to right

< > <= >= Relational left to right

== != Equality left to right

&& And left to right

|| Or left to right

? : Conditional right to left

= += -= *= /= %= Assignment right to left

53

View Flash Presentations

• Creating a workspace, project, and application

• Writing, compiling, running an application

3

• Introduction to Classes and Objects

55

3.2 Classes, Objects, Methods and Instance Variables

• Class provides one or more ______________• Method represents task in a program

– Describes the _____________ that actually perform its tasks

– Hides from its user the complex tasks that it performs

– Method _____________ tells method to perform its task

• Classes contain one or more attributes– Specified by instance variables– Carried with the object as it is used

56

3.3 Declaring a Class with a Method and Instantiating an Object of a Class

• Each class declaration that begins with keyword public

– must be stored in a _______________

– that has the same ___________ as the class and

– ends with the .__________ file-name extension.

57

Class GradeBook• keyword public is an ___________ modifier

• Class declarations include:

– Access modifier

– Keyword class

– Pair of left and right braces

• Method declarations

– Keyword ____________ indicates method is available to public

– Keyword void indicates _______________

– Access modifier, return type, name of method and parentheses comprise method header

58

Class GradeBookTest

• Java is ______________________

– Programmers can create new classes

– Test program the GradeBook class

• Class instance creation expression

– Keyword _____________

– Then name of class to create and parentheses

• Calling a method

– Object _______________, then dot separator (.)

– Then method name and parentheses

59

Compiling an Application with Multiple Classes

• Note we have two classes– Gradebook

– GradeBookTest

• Compiling multiple classes– Use the compile command in the IDE

– Compile each file ___________ (or use Compile Project command)

• Requires a ____________ in some IDE’s

60

3.4 Declaring a Method with a Parameter

• Method ___________________

– Additional information passed to a method

– Supplied in the method call with _________

•Scanner methods– _______________ reads next line of input

– next reads next ___________ of input

• See new improved GradeBook class, Figure 3.4 and GradeBookTest program, Figure 3.5

61

Outline

GradeBook.java

62

Notes on Import Declarations

•__________________ is implicitly imported into every program

• Default package

– Contains classes compiled in the ________________

– Implicitly imported into source code of other files in directory

• Packages unnecessary if fully-qualified names are used

63

3.5 Instance Variables, set Methods and get Methods

• Variables declared in the body of method

– Called _______________ variables

– Can only be used within that method

• Variables declared in a class declaration

– Called fields or _______________ variables

– Each object of the class has a separate instance of the variable

• Note set and get methods

64

Access Modifiers public and private

• private keyword

– Used for most instance variables

– private variables and methods are accessible only to methods of the ____________________________________

– Declaring instance variables private is known as data ____________________

• Return type

– Indicates item returned by method

– Declared in method header

65

GradeBookTest Class That Demonstrates Class GradeBook

• Default initial value– Provided for all fields not initialized

– Equal to _____________ for Strings

• Note private instance variables

– Cannot be accessed directly by ____________ of the object

– Use set methods to ____________ the value

– Use ______________ methods to retrieve the value

66

Primitive Types vs. Reference Types

• Types in Java– Primitive

•boolean, byte, char, short, _______, long, float, _______________

– Reference (sometimes called ____________ types)• Objects

• Default value of null• Used to invoke an object’s methods

67

3.7 Initializing Objects with Constructors

• Constructors

– _____________ an object of a class

– Java requires a constructor for every class

– Java will provide a default no-argument constructor if none is provided

• Called when keyword _________ is followed by the class name and parentheses

• Constructors which “incoming” initial value

68

AccountTest Class to use Class Account

• Note use of Scanner object

– Input floating point number

• Note use of ____________________ %f– Used to output floating-point numbers

– Place a decimal and a number between the percent sign and the f to mandate a ________________

69

Displaying Text in a Dialog Box

• Windows and dialog boxes– Many Java applications use these to display

output

– ________________ provides prepackaged dialog boxes called message dialogs

• Program to use dialog box

70

Displaying Text in a Dialog Box

• Package javax.swing– Contains classes to help create

_______________________________ (GUIs)

– Contains class JOptionPane• Declares static method showMessageDialog for displaying

a message dialog

71

Entering Text in a Dialog Box

• Input dialog– Allows user to input information

– Created using method _____________________ from class JOptionPane

72

Methods

Chapter 6

73

Program Modules in Java

• What we call "functions" in C++ are called "________________" in Java

• Purpose– Reuse code– ______________________ the program

• This can be done by putting the code in a method– Various objects in a program can invoke the same

method

74

Program Modules

• _______________ and ______________ technique

– Construct a large program from smaller pieces (or modules)

– Can be accomplished using methods

• ______________ methods can be called without the need for an object of the class

75

static Methods•static method (or class method)

– Applies to the class as a whole instead of a specific object of the class

– Call a static method by using the method call:_____________.methodName( arguments )

– All methods of the __________ class are static• example: Math.sqrt( 900.0 )

76

static Methods

• Method main–main is declared static so it can be invoked

_____________________________ of the class containing main

– Any class can contain a main method– The JVM invokes the main method belonging to

the class specified by the first command-line argument to the java command

77

Predefined Methods

• The Math class

• These methods are called by– The _____________ of the class– The dot . operator– The name of the ______________

• Example:double y = Math.cos(x);

78

Constants

• Constants– Keyword ___________________– Cannot be changed after initialization

• static fields (or class variables)– Are fields where one copy of the variable is

__________________ among all objects of the class

• Math.PI and Math.E are final static fields of the Math class

79

Method Declaration Syntax

modifiers returnType methodName (parameterDeclaration)

{ statements}• ___________ : describers (public, private, etc.)• returnType : type of value returned by method, or

____________ if it does not return a value• methodName : identifier that names the method• parameterDeclaration : list of parameters, separated

by _______________________• statements : define the behavior of the method

80

Method Declaration

• View declaration of methods in a class for finding maximums, Fig. 6.3– Note method for input, call of method ______________

– Note method for actual determining of maximum

• View test program, Fig 6.4– Note declaration of instance of new class– Note call of class methods

81

Alternative Method Declaration

• View alternative solution

• Declare methods in the __________________

• Have them follow method main()– Although they can be ____________ in the class

• Note they must be static

82

Declaring and Using Methods

• Three ways to call a method:– Use a method name by itself to call ____________

of the same class– Use a containing a reference to an object,

followed by a dot (.) and the method name to call a method of the referenced object

– Use the class name and a dot (.) to call a _______ method of a class

– Note: static methods cannot call non-static methods of the same class directly

83

Declaring and Using Methods

• Three ways to return control to the calling statement:

– If method does not return a result:• Program flow reaches the _________________ right

brace or …• Program executes the statement _____________;

– If method does return a result:• Program executes the statement

__________ expression;• expression is first evaluated and then its value is returned

to the caller

84

Argument Promotion

• Coercion of arguments

– _______________ arguments to appropriate type to pass to method System.out.println( Math.sqrt( 4 ) );

– Evaluates Math.sqrt( 4 )

– Then evaluates System.out.println()

85

Argument Promotion

• Promotion rules

– Specify how to convert types without data loss

Type Valid promotions

double None float double long float or double int long, float or double char int, long, float or double short int, long, float or double (but not char) byte short, int, long, float or double (but not char) boolean None (boolean values are not considered to be numbers in Java)

Type Valid promotions

double None float double long float or double int long, float or double char int, long, float or double short int, long, float or double (but not char) byte short, int, long, float or double (but not char) boolean None (boolean values are not considered to be numbers in Java)

86

Java API Packages

• _______________ classes grouped into categories of related classes– Called packages

• Called the Java Application Programming Interface (API)

• Note the often used API packages

87

Random-Number Generation

• Consider the random method in the Math class– Generates a random double 0 <= n < ______– The number can be manipulated and cast as an ______ to get desired range

– For the roll of a die1 + (int) (Math.random() * 6)

• Note Figure 6.7 and Figure 6.8

88

Game of Chance

Rules for "Craps"• Roll dice first time

– If sum equals 7 or 11, the player _________– If sum equals ____________, the player loses– Any other sum (4, 5, 6, 8, 9, 10) is that player’s

point• Keep rolling dice until…

– Sum matches player point• Player wins

– Sum equals _______• Player loses

89

Game of Chance

• Note the adapted version of Figure 6.9– An application

• Note– _____________ class variables– Public methods– The __________________ function requires Character. (a non instantiating class)

90

Scope of Declarations

• Scope of a ______________ is body of method where declaration appears

• Scope of local variable is from point of declaration to end of ________________

• Scope of label in labeled break/continue is statement enclosed by labeled statement

• Scope of local-variable in initialization of for( ) is for _______________________ and rest of header

• Scope of method or field of class is body of ____________

91

Shadowing

• A field is shadowed (or hidden) if a _____________ variable or parameter has the same name as the field

• This lasts until the local variable or parameter goes out of ______________

• View example– Figure 6.11 Variables with different scopes– Figure 6.12 Test program

92

Method Overloading

• Multiple methods with _____________ can be declared in same class

• Methods must have different ___________– Different numbers, types, order of parameters

• Example– Figure 6.13 Overload example class– Figure 6.14 Overload test program

93

Recursion

Recursive method• Calls ___________ (directly or indirectly)

through another method• Method knows how to solve only a ______

case• Method divides problem

– Base case– Simpler problem – Method now divides simpler

problem until solvable

• Recursive call• Recursive step

94

2! = 2 * 1 = 2 is returned

(a) Sequence of recursive calls.

(b) Values returned from each

recursive call.

Final value = 120

5! = 5 * 24 = 120 is returned

4! = 4 * 6 = 24 is returned

3! = 3 * 2 = 6 is returned

1 returned

5!

1

4 * 3!

3 * 2!

2 * 1!

5!

1

4 * 3!

3 * 2!

2 * 1!

5 * 4! 5 * 4!

Recursive Evaluation of 5!

95

Recursive Factorial Program

• Function factorial() in Figure 6.15

• Note– Initial call to factorial()– ____________ or base case– Recursive call

96

Recursive Fibonacci Program

• Consider function from program public long fibonacci( long n ) { // base case if ( n == 0 || n == 1 ) return n; // recursive step else return fibonacci( n - 1 ) + fibonacci( n - 2 ); } // end method fibonacci

• Note why this would be extremely _________

97

Recursive Fibonacci Program

return

return

+

+ return 1

return 1

fibonacci( 2 ) fibonacci( 1 )

fibonacci( 1 ) fibonacci( 0 )

return 0

fibonacci( 3 )

98

Recursion vs. Iteration

• Both the recursive functions shown can be done with either for or while loops

• In fact they are done more efficiently ____________

• Recursion has overhead– Processor time– Memory space

• General rule: If it can be done either recursively or iteratively … choose __________

99

Arrays

Chapter 7

100

Declaring and Creating Arrays

• Recall that an array is a collection of elements all of the _____________

• Array objects in Java must be created with the key word _______________

• Syntaxint c[] = new int [12];

• Results:– 12 integer locations are allocated– They are _____________________

(null for reference variables, false for boolean)

101

Using Arrays

• View example Figure 7.2

• Note– Declaration of the array– Allocation of memory with new– Initialization of array elements– Use of array attribute (_______________)– Printing of array contents

102

The Array Initializer• A comma separated list of expressions

– The ______________ list– Enclosed in _________________

• View the Example– Note again, how the array knows its own _______

for (int count = 0 ; count < array.length ; count++) . . .

103

Processing Elements of An Array

• Finding and using the arithmetic mean– __________________ the array, create– Read in values, ___________________– Declare a summation variable, initialize – ______________ the array, calculate average– _______________ the array– Print results, accessing the array

• See sample program

104

Histogram Program

• Use the value in the array to– Print the value– Print a string of asterisks for __________________

of size of the value

• View Figure 7.6,

105

Using Array Elements as Counters

• Recall program which tested random number generator (Figure 6.8)– Used 6 different variables– Used switch statement to increment– At the time we noted the ________________

• Consider a new version of the program– Uses _______________ to total the number of rolls

of each number 1 – 6– No ___________ statement needed

• View Figure 7.7

106

Enhanced for Statement

• Enhanced for statement– New feature of J2SE 5.0– Allows iterates through elements of an array or a

collection _______________________– Syntax

for ( parameter : arrayName )statement

– View example, Figure 7.12

107

References and Reference Parameters

• In Java, primitive-type variables are always passed by _________– Incoming data only

• Objects are not passed to methods– __________ to objects are passed– The reference is passed by value

• With a reference to the object the method can _____________ the object directly

108

References and Reference Parameters

• Passing arrays by reference– Improves _______________– Saves time

• ________________ of large array not required

– Saves _______________• Use memory already occupied by array• No new memory allocation required

– View example program, Figure 7.13

109

Using Arrays

• Sorting Arrays– Recall previous example

• Searching Arrays– ________________ search (see example)

• Step through array until desired value located

– Binary search• Array must be _________________• Look in middle, then above or below

– Look in middle of sub-section then above or below– Etc.

110

Multidimensional Arrays

• Java does not support ________________ arrays directly

• Does allow declaration of arrays whose elements are ______________!

int b[][];b = new int[ 2 ][ ]; // allocate rowsb[ 0 ] = new int[ 5 ]; // allocate columns for row 0b[ 1 ] = new int[ 3 ]; // allocate columns for row 1

111

Fig. 7.16 | Two-dimensional array with three

rows and four columns.

Multidimensional Arrays

112

Creating Two-dimensional Arrays

– Can be created dynamically– 3-by-4 array

int b[][]; b = new int[ 3 ][ 4 ];

– Rows can have different number of ____________ int b[][]; b = new int[ 2 ][ ]; // create 2 rows b[ 0 ] = new int[ 5 ]; // create 5 columns for row 0 b[ 1 ] = new int[ 3 ];

// create 3 columns for row

113

Variable-Length Argument Lists

• New feature in J2SE 5.0

• ___________________ number of arguments

• Use ellipsis (…) in method’s parameter list– Can occur _______________ in parameter list– Must be placed at the __________ of parameter list

• Array whose elements are all of the same type

• View example, Fig. 7.20

114

Using Command-Line Arguments

• Pass arguments from the command line– String args[]

• Appear after the _____________ in the java command– java MyClass a b

• _________________ of arguments passed in from command line– args.length

• First command-line argument– args[ 0 ]

115

Object Based Programming

Chapter 8

116

Contrast

• ____________________ Languages– Action oriented– Concentrate on writing ________________– Data supports the actions

• Object Oriented Languages– Concentrate on creating reference types– Look for ____________ which indicate classes

• Fields are data members• Methods support manipulation of the objects

117

Find the Objects … the Verbs

In this game, what are nouns that are potential classes?

In this game, what are nouns that are potential classes?

What are verbs that represent things that the

objects do?

What are verbs that represent things that the

objects do?

118

Abstract Data Types (ADTs)

• Classes in Java make creation of ADTs easier– Implementation details ____________ from users of

the class– Client code not dependent on ________________

• Example of a class– Figure 8.1 – Time class – keeps track of time in 24 hour format

119

Declaring Classes

• Usually data fields are specified as __________

• ______________ are declared as public

• Any class member (data or method) which does not need to be accessed outside the class should be private

• It ____________________________ which comes first, data fields or methods– The author prefers data fields first

120

Constructors

• Methods which have the same name as the _____________________

• Included in a class to ensure that instance variables contain __________________ when objects are created

• The constructor is called when a class object is created with the __________________

• Note:– Do not have the constructor return a _________

121

Using Classes

• View Figure 8.2• Note

– Creation of a time object with new– Call of the constructor– Use of public functions to ____________ the private data

values– Use of toString functions– Use of DecimalFormat class

• Advantages of classes– Simplifies client __________________ of classes– Reduces number of _______________________

122

Class Scope

• Variables and methods belong to the class's scope

• _________________ the class's scope– All class members are available, accessible

• Outside the class's scope– Client code that uses the class– Only _____________ members are available,

accessible

• Access modifiers public and private control this availability

123

Controlling Access to Members

• The following would not be allowed – why?

• The data members are ___________.

public class TimeTest2 { public static void main( String args[] ) { Time1 t = new Time1(); t.hour = 7; }}

public class TimeTest2 { public static void main( String args[] ) { Time1 t = new Time1(); t.hour = 7; }}

124

Using the this Reference

• Every object can access a reference to ______– Use the keyword this

• If a method has a ________ variable with same name as _________ variable, use the this to access the class variable

• Explicit use of this can increase program _____________ for human readers

• Note example, Figure 8.4

125

Using Overloaded Constructors

• ________________ constructors for the same class are allowed

• The _____________ of the constructors must be different– Different numbers and/or types of parameters

• See example in Figure 8.5 and 8.6

126

Using Set and Get Methods

• Private data fields manipulated only by provided _________________________– Some methods used to _________ the data values– Others used to get the values

• Return the value directly• Print the value

• Note: this is not the same as making the data values __________________– The set methods are written to ensure valid data

values

127

Composition

• A class can have references to __________________________ as members

• Example:– An alarm clock class contains a Time object as one

of its members– Employee class has Date object as one of its

members– See

• Date Class, Figure 8.7• Employee Class Figure 8.8• Employee Test program Figure 8.9

128

Enumerations – enum types

• Declared with an ___________ declaration

• A comma-separated list of enum constants

• Declares an enum class with the following restrictions:– enum types are implicitly _____________– enum constants are implicitly ______________– Attempting to create an object of an enum type with new is a compilation error

129

Enumerations – enum types•enum constants can be used anywhere

_____________ can•enum constructor

– Like class constructors, can specify ____________ and be overloaded

• See example, Figure 8.10

• Note test program, Figure 8.11

130

Enumerations – enum types•static method values

– Generated by the __________ for every enum– Returns an array of the enum’s constants in the

order in which they were declared

•static method _________ of class EnumSet– Takes two parameters, the first and last enum

constants in the desired range– Returns an EnumSet containing the constants in

that range, ________________– An enhanced _________ statement can iterate

over an EnumSet as it can over an array

131

Garbage Collection

• Garbage collection– JVM marks an object for garbage collection when there are

no more _________________ to that object– JVM’s garbage collector will retrieve those objects memory

so it can be used for other objects– See lines 27 – 32 of Figure 8.13

• _________________ method– All classes in Java have the finalize method

• Inherited from the Object class

– finalize is called by the ____________________ when it performs termination housekeeping

– finalize takes no parameters and has no return type _____________

132

static Class Members

• Normally each class object has its own copy of the instance variables

• Possible to specify a variable that is __________ by all existing objects of the class– Called a static variable– Also called a __________ variable – class wide information

• Also possible to have a static ______________– Can be called even if no object of the class has been

instantiated– Use class name, then dot, then static method name

• Note examples in Fig. 8.12, test pgm Fig. 8.13

133

static Class Members•String objects are _________________

– String concatenation operations actually result in the creation of a ___________ String object

•static methods ________________ non-static class members

– Also cannot use the ____________ reference

134

static Class Members

• static method _________ of class System– Indicates that the garbage collector should make a

best-effort attempt to reclaim objects eligible for garbage collection

– It is possible that _______ objects or only a _________ of eligible objects will be collected

• Note example call in Fig. 8.13

135

static Import

• Recall static fields and methods of class Math

• J2SE 5.0 enables importing static members as if ______________________ where used

• Note Figure 8.14import static java.lang.Math.*

136

Final Instance Variables

• Principle of least privilege– Code should have only the privilege and access it

needs to ________________, but no more

• final instance variables– Keyword ______________

• Specifies that a variable is ______ modifiable (is a constant)

– final instance variables can be initialized at their _______________________

• If they are not initialized in their declarations, they must be initialized in all constructors – Fig. 8.15

137

Software Reusability

• Many classes exist in the Java API

• Avoid "__________________"– Study capabilities of Java API– If it has a class that fits your needs, use it rather

than creating your own

138

Data Abstraction & Encapsulation

• Information hiding– Classes hide details of _______________ from

client

• Example:– Stack can be implemented with array or with linked

list– Client program which depends on one

implementation will have problems if new version with different implementation comes out

• Only use the ________________ provided

139

Object Oriented Programming: Inheritance

Chapter 9

140

Introduction

• Software Reusability– saves __________ in program development– encourages use of proven, ____________ code– reduces problems

• Write programs in ____________ fashion

• Enables software designers to deal with complexity of modern software

141

Introduction

• When creating a new class …– designate that class to ___________ data

members, functions of previously defined superclass

– result is a ___________________

• Subclass ____________ new data members and functions

• ________________ and refine existing members

142

Base Classes & Derived Classes

• Superclass is more ______________– student, shape, loan

• ________________ is more specific– grad student, undergrad– circle, triangle, rectangle– carloan, home improvement, mortgage

• Some languages talk of– ______________ class (Superclass)– Derived class (Subclass)

143

Superclass and Subclass

• Inheritance produces _________ like structures

144

Superclass and Subclass

• Inheritance produces tree like structures

145

Design Tip

• Important link between subclass and superclass– The “_____________” relationship

• Examples– A checking account IS-A banking account– A savings account IS NOT a checking account

• If there is no IS-A relationship, do not use __________________

146

protected Members

•protected access– ______________ level of protection between public and private

– protected members accessible by• superclass members• _________________ members• Class members in the same package

– Subclass access to superclass member• Keyword _____________ and a dot (.)

147

Comments on Private vs. Protected

• Use protected when – Superclass should provide a _____________ only

to its subclasses– Should not provide service to other clients

• Use private so that– ________________ implementation can change

without affecting subclass implementations

• Author advocates ______________ protected– Instead provide set and get methods to access

private data items (see Figures 9.12, 9.13 in text)

148

Relationship between Superclasses and Subclasses

• Superclass and subclass relationship– Example: CommissionEmployee/BasePlusCommissionEmployee inheritance hierarchy•CommissionEmployee

– First name, last name, SSN, commission rate, gross sale amount

•BasePlusCommissionEmployee– First name, last name, SSN, commission rate, gross sale

amount– Base salary

149

Creating and Using a CommissionEmployee Class

• Class CommissionEmployee– Extends class Object

• ______________________ extends• Every class in Java extends an existing class

– Except Object

• Every class inherits __________________ methods

• New class _________________ extends Object– If it does not extend another class

150

Creating and Using a CommissionEmployee Class

• Class CommissionEmployee– Extends class Object

• Keyword extends• Every class in Java extends an existing class

– Except Object

• Every class inherits Object’s methods• New class implicitly extends Object

– If it does not extend another class

• View class Figure 9.4

• View test program, Figure 9.5

151

Creating a BasePlusCommissionEmployee

Class without Using Inheritance• Class BasePlusCommissionEmployee

– Implicitly extends Object– Much of the code is similar to

CommissionEmployee•private ____________ variables•public methods• constructor

– ____________•private instance variable baseSalary• Methods setBaseSalary and getBaseSalary

152

Creating a CommissionEmployee-BasePlusCommiionEmployee Inheritance

Hierarchy

• Class BasePlusCommissionEmployee2– Extends class CommissionEmployee– Is a CommissionEmployee– Has ___________ variable baseSalary– _____________ public and protected

members– _______________ not inherited

• Note these points plus invalid references, Figure 9.8 – note compiler error messages

153

Using protected Instance Variables

• Use protected instance variables– Enable class BasePlusCommissionEmployee to

__________________ superclass instance variables

– Superclass’s protected members are inherited by all subclases of that superclass

• View version that now works, Figure 9.10

• Test program, Figure 9.11

154

Using protected Instance VariablesAdvantages

• Subclasses can _________________ values directly

• Slight __________________ in performance– Avoid set/get method call overhead

155

Using protected Instance VariablesDisadvantages

• No ________________ checking– subclass can assign illegal value

• Implementation dependent– subclass methods more likely __________ on

superclass implementation– superclass implementation changes may result in

subclass ___________________• Fragile (brittle) software

156

Reexamine Hierarchy

• Use the best software engineering practice– Declare instance variables as private– Provide public _____________________ methods– Use _____________ method to obtain values of

instance variables

• View new version of CommissionEmployee, Figure 9.12

• New version of BasePlusCommissiionEmployee, Figure 9.13


157

Instantiating Subclass ObjectChain Of Constructor Calls

• Subclass constructor invokes superclass constructor– __________ or _________________

• Base of inheritance hierarchy– Last constructor called in chain is _________________

constructor– _______________ subclass constructor’s body finishes

executing last

158

Instantiating Subclass ObjectChain Of Constructor Calls

• Example, Figure 9.15 : CommissionEmployee3-BasePlusCommissionEmployee4 hierarchy– CommissionEmployee3 constructor called second last

(last is Object constructor)– CommissionEmployee3 constructor’s body finishes

execution second (first is Object constructor’s body)

• Figure 9.16, BasePlusCommissionEmploye5• Figure 9.17, Test program, demonstrates

constructor calls

159

Software Engineering with Inheritance

• At the design stage, certain classes found to be closely related– _______________ common attributes, behaviors– Place these in a ____________________– Use inheritance to develop subclasses with

inherited capabilities

• This avoids _____________ of classes, "reinventing the wheel"

• Note– Declaring a subclass ______________________

superclass source code

160

Object-Oriented Programming: Polymorphism

Chapter 10

161

Problem with Subclasses• Given the class hierarchy below• Consider the existence of a draw function for each

subclass• Consider also an _____________________ to the

superclass (which can also point to various objects of the subclasses)

• How do you specify which __________ statement to be called when using the references

Shape class hierarchy

Circle

Right Triangle Isosceles Triangle

Triangle

Square

Rectangle

Shape

162

Introduction

• Polymorphism– Enables “programming in the ______________”– The same invocation can produce

“____________________” of results

• Interfaces– Implemented by classes to assign common

functionality to possibly unrelated classes

163

Polymorphism

• When a program invokes a method through a superclass variable,

– the correct ______________ version of the method is called,

– based on the __________________ stored in the superclass variable

• The same method name and signature can cause different actions to occur,

– depending on the ________________ on which the method is invoked

164

Polymorphism

• Polymorphism enables programmers to deal in generalities and – let the ______________ environment handle the

specifics.

• Programmers can command objects to behave in manners appropriate to those objects, – ___________________ the types of the objects – (as long as the objects belong to the same

inheritance hierarchy).

165

Polymorphism Promotes Extensibility

• Software that invokes polymorphic behavior– independent of the ________________ to which

messages are sent.

• New object types that can respond to existing method calls can be – incorporated into a system without requiring

modification of the ____________________. – Only client code that ______________ new objects

must be modified to accommodate new types.

166

Demonstrating Polymorphic Behavior

• A superclass reference can be aimed at a ______________ object

– a subclass object “is-a” superclass object – the type of the actual referenced _____________,

not the type of the _____________, determines which method is called

• A subclass reference can be aimed at a superclass object only if the object is _________________

• View example, Figure 10.1

167

Polymorphism

• Promotes _____________________

• New objects types can respond to ______________ method calls– Can be incorporated into a system without

modifying base system

• Only client code that instantiates the new objects must be modified – To accommodate ________________

168

Abstract Classes and Methods

• Abstract classes – Are superclasses (called abstract superclasses)– Cannot be _______________________ – Incomplete

• subclasses fill in "missing pieces"

• _______________________ classes– Can be instantiated– ________________ every method they declare– Provide specifics

169

Abstract Classes and Methods

• Purpose of an abstract class– Declare common ________________ …– Declare common behaviors of classes in a class

hierarchy

• Contains one or more abstract _____________– Subclasses must ______________

• Instance variables, concrete methods of abstract class– subject to normal rules of ______________

170

Abstract Classes• Classes that are too ____________ to create

real objects

• Used only as abstract superclasses for concrete subclasses and to declare ___________________

• Many inheritance hierarchies have abstract superclasses occupying the top few levels

171

Keyword abstract

• Use to declare a class abstract• Also use to declare a _____________ abstract

• Abstract classes normally contain one or more abstract _______________

• All _____________ subclasses must override all inherited abstract methods

172

Abstract Classes and Methods•Iterator class

– __________________ all the objects in a collection, such as an array

– Often used in polymorphic programming to traverse a collection that contains references to objects from various levels of a hierarchy

173

Abstract Classes

• Declares common attributes and behaviors of the various classes in a class hierarchy.

• Typically contains one or more abstract _______________ – __________________ must override if the

subclasses are to be concrete.

• Instance variables and concrete methods of an abstract class subject to the normal rules of inheritance.

174

Beware! Compile Time Errors

• Attempting to ______________ an object of an abstract class

• Failure to ______________ a superclass’s abstract methods in a subclass – unless the subclass is also declared abstract.

175

Creating Abstract Superclass Employee

•abstract superclass Employee,Figure 10.4– earnings is declared abstract

• ______________________ can be given for earnings in the Employee abstract class

– An array of Employee variables will store _____________ to subclass objects•earnings method calls from these variables will call the

appropriate version of the earnings method

176

Example Based on Employee

Abstract Class

Concrete Classes

177

Polymorphic interface for the Employee hierarchy classes.

178

Note in Example Hierarchy

• Dynamic binding– Also known as _____________ binding– Calls to overridden methods are resolved at

______________ time, based on the type of object referenced

• instanceof operator– Determines whether an _____________ is an

instance of a certain type

179

How Do They Do That?

• How does it work?– Access a derived object via __________________– Invoke an abstract method– At run time the __________________ of the

method is used

• Design of the V-Table– Note description from C++

180

Note in Example Hierarchy• Downcasting

– Convert a reference to a superclass to a reference to a subclass

– Allowed only if the object has an_____________relationship with the subclass

• getClass method– Inherited from __________________– Returns an object of type Class

• _______________ method of class Class– Returns the class’s name

181

Superclass And Subclass Assignment Rules

• Assigning a superclass reference to superclass variable straightforward

• Subclass reference to subclass variable straightforward

• Subclass reference to superclass variable ________ – because of is-a relationship– Referring to subclass-only members through superclass

variables a compilation error

• Superclass reference to a subclass variable a ___________________– Downcasting can get around this error

182

final Methods and Classes

•final methods– Cannot be ______________ in a subclass– ___________ and __________ methods implicitly final

– final methods are resolved at __________ time, this is known as static binding• Compilers can optimize by inlining the code

•final classes– Cannot be _____________ by a subclass– All methods in a final class implicitly final

183

Why Use Interfaces

• Java has single _____________, only

• This means that a child class inherits from only one parent class

• Sometimes multiple inheritance would be convenient

• Interfaces give Java some of the advantages of multiple inheritance without incurring the disadvantages

184

What is an Interface?

• An interface is a collection of _____________ and method declarations

• The method declarations do not include an _________________ (there is no method body)

185

What is an Interface?

• A child class that extends a parent class can also _____________ an interface to gain some additional behavior

• Implementing an interface is a “______________” to include the specified method(s)

• A method in an interface cannot be made ________________

186

When A Class Definition Implements An Interface:

• It _____________________ each method in the interface

• Each method must be public (even though the interface might not say so)

• ________________ from the interface can be used as if they had been defined in the class (They should not be re-defined in the class)

187

Declaring Constants with Interfaces

• ________________ can be used to declare constants used in many class declarations

– These constants are implicitly public, static and final

– Using a __________________ declaration allows clients to use these constants with just their names

188

Implementation vs. Interface Inheritance

ImplementationInheritance

• Functionality ______ in the hierarchy

• Each new subclass inherits one or more methods declared in superclass

• _____________ uses superclass declarations

Interface Inheritance

• Functionality lower in hierarchy

• Superclass specifies one or more _________ methods

• Must be declared for each class in hierarchy

• Overridden for subclass-specific implementations

189

Creating and Using Interfaces

• Declaration begins with ________________ keyword

• Classes implement an _____________ (and its methods)

• Contains __________________ methods– Classes (that implement the interface) must

implement these methods

190


• Consider the possibility of having a class which manipulates mathematical functions

• You want to send a function as a parameter– Note that C++ allows this directly– Java does not

• This task can be accomplished with interfaces

191


• Declare interface Function• Declare class MyFunction which implements Function

• Note other functions which are subclass objects of MyFunction

• View test program which passes Function subclass objects to function manipulation methods

192

Graphical User Interface Components: Part 1

Chapter 11

193

Graphical User Interface (GUI)

• Gives program distinctive “______________”

• Provides users with basic level of familiarity

• Built from GUI ________________ (controls, widgets, etc.)– User interacts with GUI component via mouse,

keyboard, etc

• Check out this visual index of components

http://java.sun.com/docs/books/tutorial/uiswing/components/components.html

194

Netscape Window With GUI Components

menu barbutton combo boxmenus

scroll bars

195

Dialog Boxes

• Used by applications to interact with the user

• Provided by Java’s JOptionPane class– Contains input dialogs and message dialogs

• View example program, Figure 11.2

196

Dialog Boxes

• Note icon

• Other icons available

Message dialog type Icon Description

ERROR_MESSAGE

A dialog that indicates an error to the user.

INFORMATION_MESSAGE

A dialog with an informational message to the user.

WARNING_MESSAGE

A dialog warning the user of a potential problem.

QUESTION_MESSAGE

A dialog that poses a question to the user. This dialog normally requires a response, such as clicking a Yes or a No button.

PLAIN_MESSAGE no icon A dialog that contains a message, but no icon.

197

Some Basic GUI Components

Component Description

JLabel Displays uneditable text or icons.

JTextField Enables user to enter data from the keyboard. Can also be used to display editable or uneditable text.

JButton Triggers an event when clicked with the mouse.

JCheckBox Specifies an option that can be selected or not selected.

JComboBox Provides a drop-down list of items from which the user can make a selection by clicking an item or possibly by typing into the box.

JList Provides a list of items from which the user can make a selection by clicking on any item in the list. Multiple elements can be selected.

JPanel Provides an area in which components can be placed and organized. Can also be used as a drawing area for graphics.

Component Description

JLabel Displays uneditable text or icons.

JTextField Enables user to enter data from the keyboard. Can also be used to display editable or uneditable text.

JButton Triggers an event when clicked with the mouse.

JCheckBox Specifies an option that can be selected or not selected.

JComboBox Provides a drop-down list of items from which the user can make a selection by clicking an item or possibly by typing into the box.

JList Provides a list of items from which the user can make a selection by clicking on any item in the list. Multiple elements can be selected.

JPanel Provides an area in which components can be placed and organized. Can also be used as a drawing area for graphics.

198

Overview

• Swing GUI components– Declared in package __________________– Most are ____________ Java components– Part of the Java Foundation Classes (JFC)

• Abstract Window Toolkit (AWT)– ___________________ to Swing– Declared in package java.awt– Does not provide consistent, cross-platform look-

and-feel

199

Lightweight vs. Heavyweight

• Lightweight components– Not tied directly to ________________________

supported by underlying platform

• Heavyweight components– Tied directly to the ____________ platform– AWT components– Some Swing components

200

Superclasses of Swing’s Lightweight GUI Components

• Class Component – (package java.awt)– ______________________ of Object– Declares many behaviors and attributes common to

GUI components

201


• Class Container – (package java.awt)– Subclass of Component– _____________________ Components

202


• Class JComponent – (package javax.swing)– Subclass of Container– _________________ of all lightweight Swing

components

203

Common Lightweight Component Features

• Pluggable look-and-feel – _______________ the appearance of components

• Shortcut keys – mnemonics

• Common ____________________ capabilities

• Brief description of component’s purpose – tool tips

• Support for _____________________

204

Displaying Text and Images in a Window

• Class JFrame– Most windows are an instance or subclass of this

class– Provides _______________________– Provides min, max, close ______________

• Label– ______________________ or information stating

the purpose of each component– Created with class JLabel

205

Three Parts of a GUI Application

1. ________________________ that make up the Graphical User Interface

2. ________________ that receive the events and respond to them

3. ____________________ that does useful work for the user

206

Events Generated by Swing Components

Act that results in the event Listener type

User clicks a button, presses Return while typing in a text field, or chooses a menu item

User closes a frame (main window) WindowListener

User presses a while the cursor is over a component

MouseListener

User over a component

MouseMotionListener

Component becomes visible ComponentListener

Component gets the keyboard focus FocusListener

Table or list selection changes ListSelectionListener

207

Events Generated by Swing Components

• Each __________ is represented by an object – Object gives information about the event – Identifies the event _________________.

• Event sources are typically _____________, – Other kinds of objects can also be event sources.

• Each event source can have _____________ listeners registered on it. – Conversely, a

single listener can register with multiple event sources.

208

JLabel

• Label– Provide ________________ on GUI– Defined with class JLabel– Can display:

• Single line of read-only text• __________________________• Text and image

• View Figure 11.6 – Note uses of the JLabel Class

209

Creating and Attaching label1

• Method setToolTipText of class JComponent

– Specifies the tool tip

• Method add of class Container– Adds a _________________ to a container

210


• Interface Icon– Can be added to a ________________ with

the setIcon method– Implemented by class ImageIcon

211


• Interface SwingConstants– Declares a set of

___________________________________ such as those used to set the alignment of components

– Can be used with methods setHorizontalAlignment and setVerticalAlignment

212


• Other JLabel methods– getText and ____________________

• For setting and retrieving the text of a label

– getIcon and setIcon• For setting and retrieving the _______________

displayed in the label

– getHorizontalTextPosition and setHorizontalTextPosition• For setting and retrieving the horizontal position of the

text displayed in the label

213

Some basic GUI Components.

Constant

Description

Horizontal-position constants

SwingConstants.LEFT Place text on the left. SwingConstants.CENTER Place text in the center. SwingConstants.RIGHT Place text on the right.

Vertical-position constants

SwingConstants.TOP Place text at the top. SwingConstants.CENTER Place text in the center. SwingConstants.BOTTOM Place text at the bottom.

214

Other JFrame Methods

• setDefaultCloseOperation– Dictates how the

____________________________ when the user clicks the close button

• setSize– Specifies the width and height of the __________

• setVisible– Determines whether the window is displayed (true)

or not (false)

215

Event Handling

• An event occurs every time the user– ________________ a character or – Pushes a _________________________

• Any object can be ________________ of the event.

• That object must:– ________________ the appropriate interface – Be registered as an event _____________ on the

appropriate event source.

216

Event Handling

• GUI's are _______________ driven– Events occur when user interacts with GUI– e.g., moving mouse, pressing button, typing in text

field, etc.

• Class java.awt.AWTEvent• Checkout Sun tutorial on event handling

http://java.sun.com/docs/books/tutorial/uiswing/overview/event.html

217

Some Event Classes Of Package java.awt.event

218

Event Handling Model

• Three parts– Event _________________

• GUI component with which user interacts

– Event _________________• Encapsulates information about event that occurred

– Event _________________• Receives event object when notified, then responds

• Programmer must perform two tasks– ____________ event listener for event source– Implement event-handling method (event handler)

219

Event Listener Object

• When a GUI program is running, each action of the user generates an event

• The following are some types of events: – Moving the ______________ – Clicking the mouse on a button – ______________ some text into a text area

• For a program to respond to an event there must be an ____________ object in the GUI program that listens to that type of event

220

What is an Event Listener?

• An event listener is an _____________ – It "listens" for events from a specific GUI component

(itself an object)

• When an event is generated by the GUI component– A ____________ in the listener object is invoked to

respond to the event

221

What If …?

• When there is no event ______________ for an event – A program can ____________ events – If there is no listener for an event, the event is just

ignored

222

Event-listener

Interfaces Of Package java.awt.event

223

Textfields

• JTextField– __________ area in which user can enter text

• JPasswordField– Extends JTextField– ______________ characters that user enters

• View Figure 11.9– Illustrates capabilities of textfields– Note help on handling number fields

224

How Event Handling Works

• You must ______________ the event handler– Through component’s method addActionListener

225

How Event Handling Works

• The component knows to call actionPerformed because …– Event is _______________ only to listeners of

appropriate type– Each event type has corresponding event-listener

interface• Event _____________ specifies event type that occurred

226

Event Registration for JTextField textField1

227

JButton

• Button– Component user clicks to trigger a specific action– Several different types

• Command ________________• Check ________________• Toggle buttons• __________________ buttons

– javax.swing.AbstractButton subclasses• Command buttons are created with class JButton• Generate __________________________ when user

clicks button

228

Swing Button Hierarchy

229

JButton Example

• View, ButtonFrame class, Figure 11.15


• Look for– Declaration of the buttons– Inner class ButtonHandler which does event

handling for the button– Call to .addActionListener(handler) method

registers buttons to receive events– The actionPerformed() method

230

Comments on JButton• To detect when user clicks button

– Program must have an _______________ that implements ActionListener interface

• Program must __________ object as an action listener on the button (the event source) – Using the addActionListener method

231

Comments on JButton• When user clicks the button, it fires an action

_________________. – Results in the invocation of the action listener's actionPerformed _____________

– The only method in the ActionListener interface

•JButtons can have a __________ icon– Appears when mouse is positioned over a button– Added to a JButton with method setRolloverIcon

232

Buttons That Maintain State

• Swing contains three types of ____________ buttons

•JToggleButton, JCheckBox and JRadioButton•JCheckBox and JRadioButton are

______________ of JToggleButton

233

JCheckBox

• Contains a check box ______________ that appears to right of check box by default

• Generates an ItemEvent when it is ____________

– ItemEvents are handled by an ItemListener– Passed to method _______________________

• Method isSelected returns whether check box is selected (true) or not (false)

• View example class Figure 11.17test Figure 11.18

234

JRadioButton

• Has two states – selected and unselected• Normally appear in a _____________ in which

only one radio button can be selected at once– Group maintained by a ButtonGroup object

• Declares method add to add a JRadioButton to group

• Usually represents mutually ____________ options

• View RadioButtonFrame, Figure 11.19Test program, Figure 11.20

235

Demonstration of JRadioButton

• When viewing Figure 11.19, look for the following– Declaration of JRadioButton references– Group specification– Instantiation of JRadioButton objects– Registration of JRadioButton's to receive events– RadioButtonHandler invokes method itemStateChanged

236

JComboBox

• JComboBox– List of items from which user can select– Also called a drop-down list

• Note features in Figure 11.21

• Instantiate JComboBox to show three Strings from names array at a time

• Register JComboBox to receive events

• ItemListener invokes method itemStateChanged

237

JList

• A list is a series of items– User can _____________ one or more items– Single-selection vs. multiple-selection

• JList demonstration, Figure 11.23– Note use of ColorNames array to populate JList– Specification of SINGLE_SELECTION– Registration of JList to __________ events– ListSelectionListener invokes method valueChanged

– Background set according to user choice

238

Multiple-Selection Lists

• Multiple-selection list capabilities– Select ______________ items from Jlist– Allows continuous _________ selection

• Look for the following in Figure 11.25

• Use of ColorNames array– Specification of MULTIPLE_INTERVAL_SELECTION

option– Use of JButton and JListCopyList method

239

Mouse Events

• Create a MouseEvent object

• Handled by MouseListeners and MouseMotionListeners

• MouseInputListener combines the two interfaces

• Interface MouseWheelListener declares method mouseWheelMoved to handle MouseWheelEvents

240

Mouse Event Handling

• Event-listener interfaces for mouse events– MouseListener– MouseMotionListener– Listen for MouseEvents

• In Figure 11.28 note use of…– Register JFrame to receive mouse events– Methods invoked for various mouse events

• (Note that program does not seem to perform as advertised when run under ReadyTo !!?)

241

Listener Interfaces

MouseListener and MouseMotionListener interface methods

Methods of interface MouseListener

public void mousePressed( MouseEvent event )

Called when a mouse button is pressed while the mouse cursor is on a component.

public void mouseClicked( MouseEvent event )

Called when a mouse button is pressed and released while the mouse cursor remains stationary on a component. This event is always preceded by a call to mousePressed.

public void mouseReleased( MouseEvent event )

Called when a mouse button is released after being pressed. This event is always preceded by a call to mousePressed and one or more calls to mouseDragged.

public void mouseEntered( MouseEvent event )

Called when the mouse cursor enters the bounds of a component.

242

Listener Interfaces

MouseListener and MouseMotionListener interface methods

public void mouseExited( MouseEvent event )

Called when the mouse cursor leaves the bounds of a component.

Methods of interface MouseMotionListener

public void mouseDragged( MouseEvent event )

Called when the mouse button is pressed while the mouse cursor is on a component and the mouse is moved while the mouse button remains pressed. This event is always preceded by a call to mousePressed. All drag events are sent to the component on which the user began to drag the mouse.

public void mouseMoved( MouseEvent event )

Called when the mouse is moved when the mouse cursor is on a component. All move events are sent to the component over which the mouse is currently positioned.

243

Listener Interfaces

• Suppose your class directly implements MouseListener, – Then you ___________________ all five MouseListener methods.

– Even if you care only about mouse clicks

• Methods for those events you don't care about can have ______________ bodies. – Resulting collection of empty method bodies can

make code harder to read and maintain

244

Adapter Classes

• Solution is to use __________________ classes

• For example, the MouseAdapter class implements the MouseListener interface.

• An adapter class implements ____________ of all its interface's methods.

245

Adapter Classes

• To use an adapter– Create a ________________ of it, instead of

directly implementing a listener interface. – By extending MouseAdapter, your class

_________________ empty definitions of all five of the methods that MouseListener contains.

246

Adapter Classes

• Characteristics of an adapter class– _________________ interface– Provides ________________ implementation of

each interface method– Used when all methods in interface is not needed

Event-adapter class in java.awt.event Implements interface

ComponentAdapter ComponentListener ContainerAdapter ContainerListener FocusAdapter FocusListener KeyAdapter KeyListener MouseAdapter MouseListener MouseMotionAdapter MouseMotionListener WindowAdapter WindowListener

247

Adapter Classes

• Example of use of an adapter class– Figure 11.34 , the Painter program

• Note– Registration of MouseMotionListener to listen

for window’s __________________ events– ____________________ method mouseDragged,

but not method mouseMoved– Store ________________ where mouse was

dragged, then repaint JFrame

248

Extending MouseAdapter

• The MouseDetails.java program, Note example, Figure 11.31

• Demonstrates– How to determine the __________ of mouse clicks– How to distinguish between _______________

mouse buttons

249

InputEvent Methods

• Help distinguish among – left-, – center- and – right-mouse-button clicksInputEvent method Description

isMetaDown() Returns true when the user clicks the right mouse button on a mouse with two or three buttons. To simulate a right-mouse-button click on a one-button mouse, the user can hold down the

Meta key on the keyboard and click the mouse button.

isAltDown() Returns true when the user clicks the middle mouse button on a mouse with three buttons. To simulate a middle-mouse-button click on a one- or two-button mouse, the user can press the Alt key on the keyboard and click the only- or left-mouse button, respectively.

250

Key Event Handling

• Interface KeyListener• Handles key events

– Generated when keys on keyboard are pressed and released

• KeyEvent– Contains ___________________ that represents

key

• Demonstrated in Figure 11.36

251

Layout Managers

• Layout manager capabilities– Provided for _________________ GUI components– Provide basic layout capabilities– Processes layout details– Programmer can concentrate on basic “look and

feel”– Interface LayoutManager

252

Layout Managers

• Layout manager methods

Layout manager Description

FlowLayout Default for javax.swing.JPanel. Places components sequentially (left to right) in the order they were added. It is also possible to specify the order of the components by using the Container method add, which takes a Component and an integer index position as arguments.

BorderLayout Default for JFrames (and other windows). Arranges the components into five areas: NORTH, SOUTH, EAST, WEST and CENTER.

GridLayout Arranges the components into rows and columns.

253

FlowLayout

• _____________________ layout manager

• GUI components placed in container from _________ to ______________

• Example program, Figure 11.39– Layout set as FlowLayout– Note results as user presses button

254

BorderLayout

• Arranges components into five ___________– NORTH (top of container)– SOUTH (bottom of container)– EAST (left of container)– WEST (right of container)– CENTER (center of container)

• View example, Figure 11.41

255

GridLayout

• Divides container into grid of specified ___________________________

• Components are added starting at top-left cell– Proceed left-to-fight until ____________ is full

• GridLayout demonstration, Figure 11.43– Clicking buttons toggles between different layouts

256

Panels

• Helps organize components

• Class JPanel is ____________ subclass

• May have components (and other _____________) added to them

• Panel example, Figure 11.45

257

Applying Concepts

• Suppose you wish to have a GUI which accomplishes the following– Enter numbers

in text boxes– Press button

to do calculations

258

Step By Step

• View code to create the window

• Note– Class (program) extends JFrame– Constructor sets up window using methods

inherited from JFrame– Method main()instantiates class object

259

Add the Text Labels

• View additional code

• Note– Declaration, instantiation of JLabels– Container reference, pane

Gets handle for contentPane– pane layout specified– JLabels added

260

Add the Text Boxes

• View next iteration of code for adding the JTextFields

• Note– Declaration, instantiation of JTextFields– Change grid layout of pane for 2 columns– Adding to pane

261

Final Version

• View final code version• Note

– Declaration, instantiation of buttons– Declaration, definition, instantiation of action

handlers• Different author, does not use inner anonymous classes

– Add action handlers to the buttons

• Our program never actually calls the action handlers

262

Implement an Event Handler Every event handler requires three bits of code:

1. Code that specifies that the class either 1. Implements a listener interface or 2. Extends a class that implements a listener interface.

For example:

public class MyClass implements ActionListener {… 2. Code that registers an instance of the event

handler class as a listener upon one or more components. For example: someComponent.addActionListener(instanceOfMyClass);

3. Code that implements the methods in the listener interface. For example: public void actionPerformed(ActionEvent e) { ...//code that reacts to the action... }

263

Exception Handling

Chapter 13

264

Motivation

• We seek programs• When something unexpected occurs

– Ensure program ________________________ the problem– Then program must do something about it

• Extensive testing of special situations can result in "____________________ code"

• Need mechanism to check for problem where it could occur

• When condition does occur– Have _________________ to code to handle the problem

265

Overview

• Exception– Indication of ___________________ during execution

• Uses of exception handling– Process exceptions from program components– Handle exceptions in a uniform manner ______________– Remove ___________ code from “main line” of execution

• A method detects an error and throws an exception– Exception handler processes the error– Uncaught exceptions yield _____________ effects

• Might terminate program execution

266

Overview

• Code that could generate errors put in ________ blocks – Code for error handling enclosed in a __________

clause– The ____________ clause always executes

• Termination model of exception handling– The block in which the exception occurs expires

• throws clause specifies _____________ method throws

267

Exception Handler

Exception "thrown" here

Exception handler

Exception handler

Thrown exception matched against first set of exception handlers

If it fails to match, it is matched against set of handlers, etc.

If exception matches ___________ of handlers, program is abandoned

268

Example

• Consider the problem of division by zero

• Note elements of Figure 13.1– try block– Following catch blocks– throws specification

269

Sequence of Events for throw

Preceding step

try block

throw statement

unmatched catch

matching catch

unmatched catch

next step

270

Sequence of Events for No throw

Preceding step

try block

throw statement

unmatched catch

matching catch

unmatched catch

next step

271

Java Exception Hierarchy

• __________________ Throwable– Subclass ________________

• Exceptional situations• Should be caught by program

– Subclass ______________• Typically not caught by program

• Checked exceptions– Catch or _________________

• Unchecked exceptions

272

Inheritance hierarchy for class Throwable

Throwable

Exception Error

AWTError ThreadDeathIOExceptionRuntimeException OutOfMemoryError

273

Handling Exceptions

• Rethrow exception if catch cannot handle it

• Resource leak– Caused when _____________________________

by a program

• The finally block– Appears after catch blocks– Always ________________– Optional– Use to release resources

274

Using finally

• View program, Figure 13.3• Note

– __________________ of exception– Code for throw exception– Blocks using ________________

• Suggestion– Do not use a try block for ____________________

which may cause a problem– Enclose _____________________ of statements– Follow by _______________ catch blocks

275

Sequence of Events for finally clause

Preceding step

try block

throw statement

unmatched catch

matching catch

unmatched catch

next step

finally

276

Stack Unwinding

• Exception not caught in scope– Method _________________– Stack ______________________ occurs– Another attempt to catch exception

• View Figure 13.4

• Note– Sequence of events during run– Resulting output

277

printStackTrace, getStackTrace and getMessage

• Throwable class– Method printStackTrace

• Prints method call __________________

– Method getStackTrace • Obtains stack-trace information

– Method getMessage• Returns _____________________ string

• View example of these, Figure 13.5

278

Chained Exceptions

• Useful for a catch handler to– Catch one exception type– Then throw a new exception of ________________– Indicates program-specific exception

• Chained exceptions enable– Exception object to ____________________ info

• Figure 13.6 demonstrates use of chained exceptions

279

Multithreading

Chapter 23

280

Introduction

• Consider ability of human body to ___________– Breathing, heartbeat, chew gum, walk …

• In many situations we need a computer to multitask

• Concurrency normally available in __________

• Java provides built-in multithreading– Multithreading improves the ___________ of some

programs

281

Thread States: Life Cycle of a Thread

• __________________ state– New thread begins its life cycle in the new state– Remains in this state until program starts the

thread, placing it in the runnable state

• runnable state– A thread in this state is ___________ its task

• waiting state– A thread ___________ to this state to wait for

another thread to perform a task

282

Thread States: Life Cycle of a Thread

• __________________ state– A thread enters this state to wait for another

thread or for an amount of time to elapse– A thread in this state returns to the ___________

state when it is signaled by another thread or when the timed interval expires

• terminated state– A runnable thread enters this state when it

_____________ its task

283

Operating System View Of runnable State

• ready state– ____________ waiting for another thread– Waiting for the ______________ to assign the

thread a processor

284

Operating System View Of runnable State

• running state– Currently has a _________________ and is

executing– Often executes for a small amount of processor

time called a _______________________ before transitioning back to the ready state

285

Thread Priorities and Thread Scheduling

• Java thread priority– Priority in range ______________

• Timeslicing– Each thread assigned time on the processor (called

a quantum)– Keeps ______________ threads running

286

Priorities and

Scheduling

Thread.MAX_PRIORITY

287

Creating and Executing Threads•Runnable interface

– Preferred means of creating a multithreaded application

– Declares method _______________– Executed by an object that implements the Executor interface

•Executor interface– Declares method ___________________– Creates and manages a group of threads called

a thread pool

288

Creating and Executing Threads

•ExecutorService interface– ______________________ of Executor that

declares other methods for managing the life cycle of an Executor

– Can be created using _______________ methods of class Executors

– Method shutdown _______________ when tasks are completed

289


•Executors class– Method newFixedThreadPool creates a pool

consisting of a __________________________ of threads

– Method newCachedThreadPool creates a pool that creates new threads _____________________________

290


• PrintTask class Figure 23.4

• RunnableTester, Figure 23.5

• Demonstrates– ____________ Thread objects– Using Thread methods ___________ and sleep– Creates 3 equal priority threads– Each is put to sleep for random number of

milliseconds– When awakened, it displays name, etc.

291

Producers and Consumers

• Producer– Generating

_______________

• Consumer– Receives and

_________________the output

292

Synchronization

• Problem– Sometimes the producer gets too far

____________ of the consumer • The objects produced fill up the holding area

(_____________)• The producer must wait for space to place objects

– Sometimes the ______________ gets ahead of the producer

• There are no objects to be processed (_____________ buffer)

• The consumer must wait for the producer

293

Thread Synchronization• Thread synchronization

– Provided to the programmer with _____________________• Exclusive access to a shared object

– Implemented in Java using _____________

•Lock interface– lock method obtains the lock, enforcing mutual

exclusion– unlock method ________________ the lock– Class ReentrantLock implements the Lock

interface

294

Thread Synchronization

• Condition variables– If a thread holding the lock cannot continue with its

task until a condition is satisfied, the thread can wait on a ____________________

– Create by calling Lock method newCondition– Represented by an object that implements the ___________________ interface

295

Thread Synchronization

• Condition interface– Declares methods await, to make a thread wait, – ____________________, to wake up a waiting

thread, and – signalAll, to wake up all waiting threads

296

Producer/Consumer Relationship without Synchronization

• Buffer– ____________________ memory region

• Producer thread– Generates _____________ to add to buffer– Calls wait if consumer has not read previous message in

buffer– Writes to empty buffer and calls ____________ for

consumer

• Consumer thread– Reads data from buffer– Calls wait if buffer ________________

• Synchronize threads to avoid corrupted data

297


• View source code which establishes– Buffer, Figure 23.6

• An interface which specifies get and set methods

– Producer, Figure 23.7• ___________________ of Thread• Uses a shared Buffer object• Method run is _________________ from Thread class• Uses Buffer.set() method

– Consumer, Figure 23.8• Also a subclass of Thread, also uses shared Buffer• Uses the Buffer.get() method

298


• View Figure 23.9 which implements the Buffer interface– Implements the _________________ methods

• This UnsynchronizedBuffer object is used in Figure 23.10 program– Buffer object declared, instantiated– Also Producer and Consumer objects– Both threads call method start()

299


• Example randomly called producer and consumer

• You should note that in some cases the data was _________________– Consumer reads values _________ producer

generates– Consumer _______________ a value– Consumer reads same value multiple times

• We need to deal with problem so data is not corrupted

300

Producer/Consumer Relationship with Synchronization

• Solution is to _________________ the producer and consumer objects

• Figure 23.11 implements a buffer and synchronizes – Consumer consumes only ______ produces a value– Producer produces a value only after consumer

consumes ____________ value produced– Condition variable occupiedBufferCount

determines whose turn it is

• Program which uses this, Figure 23.12

301

Using Thread Methods

• Create Wait class

• Has _______________ methods

• Provide capability to have another application ______________ for a certain amount of time

• Note Example to act as a simple timer.

302

Circular Buffer• Features

– Multiple memory cells– Produce item if one or more empty cells– Consume item if one or more filled cells

• Caveats– Producer and consumers must be relatively

______________ speed• Otherwise buffer fills up or stays empty

– Synchronization still necessary– Seek to optimize buffer size

• ______________________ thread-wait time

303

Circular Buffer

• Circular Buffer class Figure 23.13– ______________ for mutual exclusion– Condition variables to control writing and reading– Circular buffer; provides three spaces for data– Obtain the lock ____________ writing data to the

circular buffer– Wait until a buffer space is ___________– Impose circularity of the buffer– ___________ waiting thread when to read data

from buffer– Release lock

304

Circular Buffer

• Circular Buffer test, Figure 23.14– Create instance of circular buffer– Execute producer, consumer in separate threads

305

Daemon Threads

• Run for benefit of _____________________– Do not prevent program from terminating– __________________ is a daemon thread

• Set daemon thread with method setDaemon– Must be done at __________________ time

• Do not assign _____________ tasks to daemon thread– Will be terminated without warning– May prevent those tasks from completing properly

306

Runnable Interface

• May be necessary to __________ a class that already extends a class other than Thread

• Java does not allow a class to extend more than one class at a time– Implement Runnable for ____________ support

• Program that uses a Runnable object to control a thread– Creates a Thread object– Associates the Runnable object with that Thread

class

307

Runnable Interface

• Illustration of using a Runnable interface– Figure 23.18

• Note methods start, stop, run

308

Files and Streams

Chapter 14

309

Introduction

• Storage of data in variables is ___________– when the program is done running,

when computer is turned off The data is gone!

• Data stored permanently (more or less) on secondary storage devices– magnetic ____________– ___________ disks– tapes

• We consider creation & use of files of data

310

The Data Hierarchy

• Lowest level of data storage is in ____________________– 0s and 1s -- bits

• Bits grouped together into _______________• Bytes grouped into characters• Characters and/or bytes grouped together to form

_________________• Fields grouped together to form records• Records grouped to form files

311

The Data Hierarchy

312

Sequential Devices -- Some History

• Tape Drives

313

Data Stored on Tape

Interblock Gap for purpose of _______________ or deceleration of tape past the read/write head.

Result is large percentage of tape length ___________ on the gaps.

Interblock Gap for purpose of _______________ or deceleration of tape past the read/write head.

Result is large percentage of tape length ___________ on the gaps.

314

Data Stored on Tape

Records _______________ in groups to save space wasted by the required gaps

Records _______________ in groups to save space wasted by the required gaps

315

Disk Components

• Cylinders• Tracks• Sectors

316

Disk Components

• _______________ heads move in and out

• Possible to have multiple fixed heads

• Need head for each _____________ surface

• __________________ of data on inside as outside tracks

317

Disk Components

• Track• Sector• Inner sectors have

same amount of data as outer outer (why?)

• Outer sectors less ____________ (bits per inch)

318

Timing Components

• Access motion time (_____________ time)– motion of read/write heads between tracks– this is the most time of the three

• Rotational delay

• Data __________ time

319

Storage of Sequential Files

• Any type of serial access storage device– originally ___________________– magnetic tape– even punched paper tape!

• Now would be placed on __________________ devices (disks)

320

Files and Streams

• Java views a file as a stream of __________ • File ends with end-of-file marker or a specific byte

number

• File as a stream of bytes associated with an object– Java also associates streams with _____________

•System.in, System.out, and System.err• Streams can be redirected

321

Files and Streams

• File processing with classes in package java.io– FileInputStream for

____________________ input from a file– FileOutputStream for

byte-based ________________ to a file– FileReader for -based

input from a file– ________________ for character-based

output to a file

322

Files and Streams

• Buffering– ____________________ performance of I/O– Copies each output to a region of memory called a buffer

• We can send the entire buffer to disk ___________– One long disk access takes ____________________ than

many smaller ones– Due to repeated head seeks required

• BufferedOutputStream buffers file output• BufferedInputStream buffers file input

323

Class File

• Methods from class File

324

Class File

• Methods from class File

325

Class File

• View Figure 17.4– Creates a GUI with JTextField– Enter file, directory name– _________________ displays information

• Program features– Body of if outputs information about file if it exists– Test if object is ______________, test if file exists– Create a reader to gather data from file– Read text _________________ in file– Get list of files in directory

326

Creating a Sequential-Access File

• Java imposes __________________ on a file

• _______________________ structures file according to application

• AccountRecord class specified in Figure 17.6 declares structure for file access examples … note …– Class compiled into _______________– Imlements ________________ for use without

I/O streams

327


• Program in Figure 17.5 prepares GUI's for file access program

• Note– Class compiled as a package– Buttons provided for actions in later examples– Generic doTask buttons

328


• Program in Figure 17.7 imports the GUI and record classes– Interface and references to buttons created– Instantiate, assign JFileChooser object– Selected file retrieved, opened– Method closeFile to close current file– Data retrieved from text fields– New record retrieved, written to file

329

Reading Data from Sequential Access Files

• Data stored in files• Retrieved for processing when needed• Accessing a sequential file

– Data must be read in ________________ it was written

• Note program of Figure 17.9– Create instance of interface– Respond to Open button, Next button– JFileChooser used as before– Method _______________ reads an Object from the ObjectInputStream

330

Reading Data from Sequential Access Files

• To read from file repeatedly– Must close and reopen file

• Each time through– Print only records which _________________

• Figure 17.19 allows inquiries– Note ____________ of FileInputStream in ObjectInputStream

– Note use of _______________ for EOFException

331

Updating Sequential Access Files

• Difficult to ____________ a sequential-access file– Entire file must be rewritten to change one field– Only acceptable if many records being updated at

once

• Note that this was done in the days of using magnetic tapes

332

Characteristics of Sequential Systems

• Two types of files– ___________ files -- files with relatively

permanent data– Transaction files -- file of _____________ records

• Updating master files– use transaction files– combine (_____________) old master with

transaction file– create new master file– Old master and Transaction file are the

_____________ for the New Master

333

Updating Master Files

Old Master

File Transaction

Update Program Exception

Report

New Master

334

Updating Master Files

• Transaction file contains– _______________ to be added– modifications to __________ records on old master– orders for deletions of records on the old master

• Possible errors– Adding => record for specified ID __________

exists– Modify => record does not exist– _____________ => record does not exist

335

Program Flow ChartOpen files, read 1st records

Trans key > OM key

Write OM record to NM file, Trans key yet to be matched

Trans key = = OM key

Compare keys

Trans Key < OM key

Type of Trans Type of

Trans

Add OK Other, Error

Other, Error

Modify, Make changes

Del, go on

336

Sequential U

pdate

337

Sequential Update

Transaction File Old Master New Master

10 M20 M25 I30 D35 D40 A50 M55 M80 M

102030405060708090100

338

Random-Access Files

• “Instant-access” applications– Record must be located ______________– Transaction-processing systems require rapid

access

• Random-access files– Access individual records directly and quickly– Use _______________ for every record

• Easy to calculate record locations

– Insert records without ______________ other data in file

339

Java's View of Random-Access File

340

Creating a Random-Access File

• RandomAccessFile objects– Like DataInputStream and DataOutputstream

– Reads or writes data in spot specified by file-position pointer

• Manipulates all data as ____________________• Normally writes one ______________ at a time to file

• Note Figure 17.12, a new class derived from AccountRecord

341

Creating a Random-Access File

• RandomAccessAccountRecord of Figure 17.12 adds features– Two ________________________– Routine to read a record– Routine to _______________ a record

• These will be used in the application to create a Random file, Figure 17.13– Window to name and open the new file– Program generates 100 empty records

342

Writing Data Random-Access File

• Figure 17.14– Opens the file previously created– First window has ______________ button, Open

dialog box appears– Uses BankUI graphical interface– Click _______________ button to save the record

• RandomAccessFile method ____________– Determines location in file where record is stored– Sets file-position pointer to a specific point in file

343

Reading from Random-Access File

• Read through random-access file, Figure 17.15– Opens the RandomAccessFile, specify file name

with Open file dialog box– Record displayed in BankUI window– Click on _____________ button to view next record– _________________ combination handles end of

file

344

Transaction-Processing Program

• Substantial transaction-processing system, Figure 17.21 class with methods for – Uses random-access file– Updates, adds and deletes accounts

• Note– Creation of ________________ object– Handling of action buttons– Creating new records– Updating, deleting records– __________________ records in text fields

345

Transaction-Processing Program

• FileEditor program, Figure 17.22• Uses the TransactionProcessor class• Features

– Create RandomAccessFile from name provided– Position ______________________– Read, edit, – Reposition file pointer, update record– Delete record by ____________________

Documents

Chapter 1 Introduction to Java Chapter 1. 2 History of Java Java – Originally for _______________ consumer- electronic devices – Then used for creating