Chapter 2 Animated

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required for reproduction or display. Chapter 2 - 1

Chapter 2

Getting Started with Java

Animated Version


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Objectives

After you have read and studied this chapter, youshould be able to

Identify the basic components of Java programs

Write simple Java programs Describe the difference between object declaration and creation

Describe the process of creating and running Java programs

Use the Date, SimpleDateFormat, String, and Scanner standard

classes

Develop Java programs, using the incremental development

approach


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The First Java Program

The fundamental OOP concept illustrated by theprogram:

An object-oriented program usesobjects.

This program displays a window on the screen.

The size of the window is set to 300 pixels wideand 200 pixels high. Its title is set to My First Java

Program.


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Program Ch2Sample1

import javax.swing.*;

class Ch2Sample1 {

public static void main(String[ ] args) {

JFrame myWindow;

myWindow = new JFrame( );

myWindow.setSize(300, 200);

myWindow.setTitle(My First Java Program);

myWindow.setVisible(true);

}

}

Declare a name

Create an object

Use an object


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Program Diagram for Ch2Sample1

myWindow : JFrame

Ch2Sample1

setTitle(My First Java Program)


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Dependency Relationship

myWindow : JFrame

Ch2Sample1

Instead of drawing all messages, we summarize it by showing

only the dependency relationship. The diagram shows thatCh2Sample1depends on the service provided by myWindow.


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MoreExamples

Object Declaration

JFrame myWindow;

Account customer;Student jan, jim, jon;

Vehicle car1, car2;

Object NameOne object is declaredhere.

Class Name

This class must bedefined before this

declaration can be stated.


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Object Creation

myWindow = new JFrame ( ) ;

MoreExamples

customer = new Customer( );

jon = new Student(John Java);car1 = new Vehicle( );

Object NameName of the object we

are creating here.

Class Name

An instance of this classis created.

Argument

No arguments are usedhere.


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Declaration vs. Creation

Customer customer;


Customer customer;


1. The identifiercustomeris

declared and space is

allocated in memory.

2. A Customerobject is

created and the identifier

customeris set to refer to it.

1

2

customer

1

: Customer2


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State-of-Memory vs. Program

customer

: Customer

State-of-Memory

Notation

customer : Customer

Program Diagram

Notation


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Name vs. Objects

Customer customer;



Customer customer;

customer



: Customer : CustomerCreated with

the first new.

Created with the second

new. Reference to the firstCustomer object is lost.


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Sending a Message

myWindow . setVisible ( true ) ;

MoreExamples

account.deposit( 200.0 );

student.setName(john);car1.startEngine( );

Object NameName of the object to

which we are sending a

message.

Method NameThe name of the

message we are sending.

ArgumentThe argument we are

passing with the

message.


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JFrame myWindow;



myWindow.setTitle

(My First Java Program);


Execution Flow


Jframe myWindow;

myWindow


State-of-Memory Diagram

: JFrame

width

height

title

visible

200

My First Java

300

true


myWindow.setTitle

(My First Java Program);

The diagram shows only four of the many data

members of a JFrame object.

Program Code


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Program Components

A Java program is composed of

comments,

import statements, and

class declarations.


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/*Chapter 2 Sample Program: Displaying a Window

File: Ch2Sample2.java

*/


class Ch2Sample1 {


JFrame myWindow;





}

}

Program Component: Comment

Comment


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Matching Comment Markers

/* This is a comment on one line */

/*

Comment number 1

*/

/*

Comment number 2

*/

/*

/*

/*This is a comment

*/

*/

Error: No matching

beginning marker.

These are part of the

comment.


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Three Types of Comments

/*

This is a comment with

three lines of

text.

*/

Multiline Comment

Single line Comments

// This is a comment

// This is another comment

// This is a third comment

/**

* This class provides basic clock functions. In addition

* to reading the current time and todays date, you can

* use this class for stopwatch functions.

*/

javadoc Comments


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Import Statement

/*

Chapter 2 Sample Program: Displaying a Window


*/


class Ch2Sample1 {


JFrame myWindow;





}

}

ImportStatement


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Import Statement Syntax and Semantics

. ;e.g. dorm . Resident;

MoreExamples

import javax.swing.JFrame;import java.util.*;

import com.drcaffeine.simplegui.*;

Class Name

The name of the class wewant to import. Use asterisks

to import all classes.

Package Name

Name of the package thatcontains the classes we

want to use.


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Class Declaration

/*



*/


class Ch2Sample1 {


JFrame myWindow;





}

}

Class

Declaration


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Method Declaration

/*



*/


class Ch2Sample1 {


JFrame myWindow;





}

}

MethodDeclaration


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Method Declaration Elements

public static void main( String[ ] args ){

JFramemyWindow;





}

Method Body

Modifier Modifier Return Type Method Name Parameter


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Template for Simple Java Programs

/*



*/


class Ch2Sample1 {


JFrame myWindow;



myWindow.setTitle(

My First Java Program);


}

}

ImportStatements

Class Name

Comment

Method Body


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Why Use Standard Classes

Dont reinvent the wheel. When there are existingobjects that satisfy our needs, use them.

Learning how to use standard Java classes is thefirst step toward mastering OOP. Before we can

learn how to define our own classes, we need tolearn how to use existing classes

We will introduce four standard classes here: Scanner

String

Date

SimpleDateFormat.


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Standard Output

Using print ofSystem.out (an instance of thePrintStream class) is a simple way to display aresult of a computation to the user.

System.out.print(I Love Java);

The result appears onthe console window.

The actual appearance

of the console window

differs depending on

the Java tool you use

I Love Java


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Using the print Method

The print method will continue printing from theend of the currently displayed output.

System.out.print(How do you do? );

System.out.print(My name is );

System.out.print(Jon Java. );

How do you do? My name is Jon Java.


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Using the println Method

The println method will skip to the next line afterprinting out its argument.

System.out.println(How do you do? );

System.out.println(My name is );

System.out.println(Jon Java. );

How do you do?My name is

Jon Java.


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String is an Object

1. The identifiername isdeclared and space is

allocated in memory.

2. A String object is created

and the identifiername is

set to refer to it.

1

2

name

1

String name;

name = new String(Jon Java);

String name;

name = new String(Jon Java);

2

: String

Jon Java


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String Indexing

The position, or index, of

the first character is 0.


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Definition: substring

Assume str is a String object and properlyinitialized to a string.

str.substring( i, j ) will return a new string byextracting characters of str from position i toj-1where 0 i length of str, 0 j length of str,and i j.

If str is programming , then str.substring(3, 7)will create a new string whose value is gram

because g is at position 3 and m is at position6.

The original string strremains unchanged.


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Examples: substring

String text = Espresso;

text.substring(6,8)

text.substring(0,8)

text.substring(1,5)

text.substring(3,3)

text.substring(4,2)

so

Espresso

spre

error


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Definition: length

Assume str is a String object and properlyinitialized to a string.

str.length( ) will return the number of

characters in str.

If str is programming , then str.length( ) willreturn 11 because there are 11 characters in it.

The original string strremains unchanged.


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Examples: length

String str1, str2, str3, str4;

str1 = Hello ;str2 = Java ;

str3 = ; //empty string

str4 = ; //one space

str1.length( )

str2.length( )

str3.length( )

str4.length( )

5

4

1

0


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Definition: indexOf

Assume str and substr are String objects andproperly initialized.

str.indexOf( substr ) will return the first positionsubstr occurs in str.

If str is programming and substr is gram ,then str.indexOf(substr ) will return 3 becausethe position of the first character of substr in stris 3.

If substr does not occur in str, then1 isreturned.

The search is case-sensitive.


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Examples: indexOf

String str;str = I Love Java and Java loves me. ;

str.indexOf( J )

str2.indexOf( love )

str3. indexOf( ove )

str4. indexOf( Me )

7

21

-1

3

3 7 21


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Definition: concatenation

Assume str1 and str2 are String objects andproperly initialized.

str1 + str2 will return a new string that is a

concatenation of two strings.

If str1 is pro and str2 is gram , then str1 +str2 will return program.

Notice that this is an operator and not a method

of the String class. The strings str1 and str2 remains the same.


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Examples: concatenation

String str1, str2;str1 = Jon ;

str2 = Java ;

str1 + str2

str1 + + str2

str2 + , + str1

Are you + str1 + ?

JonJava

Jon Java

Java, Jon

Are you Jon?


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Date

The Date class from thejava.util package is used

to represent a date.

When a Date object is created, it is set to today

(the current date set in the computer)

The class has toString method that converts theinternal format to a string.

Date today;

today = new Date( );

today.toString( );

Fri Oct 31 10:05:18 PST 2003


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SimpleDateFormat

The SimpleDateFormat class allows the Dateinformation to be displayed with various format.

Table 2.1 page 62 shows the formatting options.

Date today = new Date( );

SimpleDateFormat sdf1, sdf2;

sdf1 = new SimpleDateFormat( MM/dd/yy );

sdf2 = new SimpleDateFormat( MMMM dd, yyyy );

sdf1.format(today);

sdf2.format(today);

10/31/03

October 31, 2003


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Reading from Standard Input

After the Scanner object is set up, we can read data. The following inputs the first name (String):

System.out.print (Enter your first name: );

Enter your first name: ENTERGeorge

Nice to meet you, George.

1. Prompt is displayed

2. Data is entered

3. Result is printed

String firstName = scanner.next();

System.out.println(Nice to meet you, +firstName +.);


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Problem Statement

Problem statement:Write a program that asks for the users first,

middle, and last names and replies with their

initials.

Example:

input: Andrew Lloyd Weber

output: ALW


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Overall Plan

Identify the major tasks the program has to

perform.

We need to know what to develop before we develop!

Tasks:

Get the users first, middle, and last names

Extract the initials and create the monogram

Output the monogram


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Development Steps

We will develop this program in two steps:

1. Start with the program template and add code to

get input

2. Add code to compute and display the monogram


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Step 1 Code

/*

Chapter 2 Sample Program: Displays the MonogramFile: Step1/Ch2Monogram.java

*/


class Ch2Monogram {

public static void main (String[ ] args) {

String name;

name = JOptionPane.showInputDialog(null,"Enter your full name (first, middle, last):);

JOptionPane.showMessageDialog(null, name);

}

}


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Step 1 Test

In the testing phase, we run the program and

verify that

we can enter the name

the name we enter is displayed correctly


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Step 2 Design

Our programming skills are limited, so we will

make the following assumptions:

input string contains first, middle, and last names

first, middle, and last names are separated by

single blank spaces Example

John Quincy Adams (okay)

John Kennedy (not okay)

Harrison, William Henry (not okay)


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Step 2 Design (contd)

Given the valid input, we can compute themonogram by breaking the input name into first, middle, and last

extracting the first character from them

concatenating three first characters

Aaron Ben Cosner

Aaron Ben Cosner

Ben Cosner

ABC


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Step 2 Test

In the testing phase, we run the program and

verify that, for all valid input values, correct

monograms are displayed.

We run the program numerous times. Seeing

one correct answer is not enough. We haveto try out many different types of (valid) input

values.


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Program Review

The work of a programmer is not done yet.

Once the working program is developed, we

perform a critical review and see if there are

any missing features or possible

improvements One suggestion

Improve the initial prompt so the user knows the

valid input format requires single spaces between

the first, middle, and last names

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Chapter 2 Animated