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Chapter 2: Java Fundamentals cont’d

Spring 2006-2007Lory Al Moakar

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Outline 2.1 The Parts of a Java Program 2.2 The print and println Methods, and the Java Standard Class

Library 2.3 Variables and Literals 2.4 Primitive Data Types 2.5 Arithmetic Operators 2.6 Combined Assignment Operators 2.7 Conversion Between Primitive Types 2.8 Creating Named Constants with final 2.9 The String Class 2.10 Scope 2.11 Comments 2.12 Programming Style 2.13 Reading Keyboard Input 2.14 Dialog Boxes 2.15 Common Errors to Avoid

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Review

Parts of the program Comments: start with //

Are ignored by the compiler Class header : public class Name Method header:

public static void main( String args[] ) Statements

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Review

System.out.print: displays on the screen what we put in “”

System.out.println: same as print except that it moves the cursor to a new line after displaying the text

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ReviewMoves the cursor to

\n a new line

\t the next tab stop

\b one character back

\r To the beginning of the line

\\ Prints a backslash

\’ Prints a single quote

\” Prints a double quotation mark

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Review

Variables: Declare: type and identifier Initialize: give it value ~ literal

Literals: Identifiers:

Start with letter, _, or $ Have only numbers, letters, _ and $ Cannot be a keyword

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Printing a variable

2 ways: On its own:

System.out.println( identifier); Combined with text:System.out.println( “The result is: “+

identifier );

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Example// This program has a variable.

public class Variable{ public static void main(String[] args) { int value;

value = 5; System.out.print("The value is "); System.out.println(value); }}

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2.4 Primitive Data Types

Each variable has a data type which is the type of data that can be stored in the memory location allocated

Here is a list of primitive(numeric) data types:

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2.4 Primitive Data Types cont’dData type

Size Range

byte 1 byte Integer between -128 to 127

short 2 bytes Integer between -215 to 215 -1

int 4 bytes Integer between -231 to 231 -1

long 8 bytes Integer between -263 to 263 -1

float 4 bytes Floating point numbers with 7 digits of accuracy

double 8 bytes Floating point numbers with 15 digits of accuracy

No digits after decimal point

15 digits after decimal point

7 digits after decimal point

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Declaration revisited

Datatype Variablename; Examples:

int hours; byte minutes; short month; float average; double distance

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The Integer Data Types// This program has variables of several of the integer types.

public class IntegerVariables{ public static void main(String[] args) { int checking; // Declare an int variable named checking. byte miles; // Declare a byte variable named miles. short minutes; // Declare a short variable named minutes. long days; // Declare a long variable named days.

checking = -20; miles = 105; minutes = 120; days = 185000; System.out.println("We have made a journey of " + miles + " miles."); System.out.println("It took us " + minutes + " minutes."); System.out.println("Our account balance is $" + checking); System.out.println("About " + days + " days ago Columbus " + "stood on this spot."); }}

We have made a journey of 105 miles.It took us 120 minutes.Our account balance is $-20.About 185000 days ago Columbus stood on this spot.No Commas

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The Floating Data Types// This program demonstrates the double data type.

public class Sale{ public static void main(String[] args) { double price, tax, total;

price = 29.75; tax = 1.76; total = 31.51; System.out.println("The price of the item " + "is " + price); System.out.println("The tax is " + tax); System.out.println("The total is " + total); }}

The price of the item is 29.75The tax is 1.76The total is 31.15

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The Floating Data Types

float number = 23.5; float number = 23.5f; float number = 23.5F;

ERROR

CORRECT

CORRECT

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The boolean Data Type a boolean variable can have two values:

true false

Example:boolean bool;bool = true;System.out.println(bool);bool = false;System.out.println(bool);

truefalse

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The char Data Type used to store characters character literals are enclosed in single

quotes Example:

char letter;letter = 'A';System.out.println(letter);letter = 'B';System.out.println(letter);

AB

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The char Data Type

Characters are internally represented by numbers.

Java uses Unicode which is a set of numbers that are used as codes for representing characters

The codes are found in appendix A on the CD

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Example

char letter; letter = 65; System.out.println(letter) letter = 66; System.out.println(letter);

A B

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Variable Assignment and Initialization

assignment statement is used to put a value into a variable. Ex: x = 15;

always put the identifier on the left of the equal sign and the literal to the right of the equal sign. Ex: 15 = x; is incorrect

you can assign the value of one identifier to another. Ex: x = y; now x has the value stored in y

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Valid Variable Declaration

int month =2, days = 28; float distance = 35.2f; int c = 8, y =10, x, v=2;

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2.5 Arithmetic Operators

3 types of operator: unary: require a single operand.

There is one unary operand: -9 (the negation operator)

--5 is 5 binary: require two operands ternary: require three operands

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Arithmetic operatorsOperator Meaning Type Example

+ Addition Binary total = cost+tax;

- Subtraction Binary cost = total-tax;

* Multiplication Binary Tax = cost*rate;

/ Division Binary saleprice=original/2;

% Modulus Binary remainder=value%3;

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Examples of Statements with Arithmetic Operators

amount = x + y; amount = 562+543; Minutes = 800 – call; Tip = bill * 0.18; Slice = cake /8;

Notice that the identifier is to the

left of the =

Notice that the arithmetic operator

is to the right of the =

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Example

int counter = 0; //counter =0counter = counter + 1; //counter =1counter = counter + 39; //counter=40counter = counter – 8; //counter=32counter = counter * 5; //counter=160counter = counter / 2; //counter= 80

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The % operator

Returns the remainder of the division Examples;

4%5 is 4 30%6 is 0 22%7 is 1 3205%100 is 5 3205%10 is 5

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Exercise

Write the following in a Java file:double amount = 137/5;

System.out.println(“Amount is : “ + amount );

amount = 137.0/5; System.out.println(“Amount is : “ +

amount );

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Integer Division

Dividing an integer by an integer gives an integer the remainder is ignored

Examples: 5/4 is 1 17/3 is 5

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Operator Precedence

What is the result of: Polynomial = 1+2*3+ 6/2 -2; Is it ?

(1+2)*3 + 6/(2-2) 1+(2*3) +(6/2)-2 (1+2)*3 + (6/2)-2

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Precedence Rules

Always evaluate * , / and % before + and –

Always negate before any calculations *, / and % have same precedence + and – have same precedence If equal precedence then evaluate

from left to right except for negations where we evaluate from right to left

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Precedence examples

Polynomial = 1+2*3+ 6/2 – 2; Polynomial has the value of 1+6+3-2=8

Polynomial = –1 + 5 – 2; // 2 Polynomial = –(–3) + –(–5); //8

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Grouping with parentheses

You can use parentheses to force the evaluation of a formula

Examples: x * ( y + z*z ) instead of x*y + z*z x * ( y * ( z + 165 ) + 85 ) – 65 Average = (a +b +c ) /3;

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The Math class

value = Math.pow( x,y); // now value holds x to the power of y

value = Math.sqrt( x); //now value holds the square root of x

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Combined Assignment Operators

+= x += 1; x = x + 1;

–= x –= 1; x = x – 1;

*= x *= 1; x = x * 1;

/= x /= 1; x = x / 1;

%= x %= 1; x = x % 1;