windows programming using java

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I N S T R U C T O R : S H I H - S H I N H H UA N G

Windows Programming Using Java

Chapter2: Introduction to Java Applications

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Contents

IntroductionA First Program in JavaText DisplayingValue Input: Integer AdditionArithmeticEquality and Relational Operators

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Introduction

Java Keywordsabstract do import public throws

boolean double instanceof return transient

break else int short trybyte extends interface static voidcase final long strictfp volatilecatch finally native super whilechar float new switch  

class for package synchronized  

continue if private this  

default implements protected throw  

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Introduction

Identifier Rule Series of characters consisting of letters,

digits, underscores ( _ ) and dollar signs ( $ )

“Welcome1”, “$value”, “_value”, “button7” are valid

“7button” is invalid Case sensitive (capitalization matters)

a1 and A1 are different

Identifier = (letter | '_' | ' $ ') {letter | digit | '_'}.

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Introduction

Primitive Data TypeData Type Purpose Contents Default Value*boolean Truth value true or false faleschar Character Unicode characters \u0000

byte Signed integer 8 bit two's complement (byte) 0

short Signed integer 16 bit two's complement (short) 0

int Signed integer 32 bit two's complement 0

long Signed integer 64 bit two's complement 0L

float Real number 32 bit IEEE 754 floating point 0.0f

double Real number 64 bit IEEE 754 floating point 0.0d

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A First Program in Java

Function: printing a line of text 1 // Fig. 2.1: Welcome1.java 2 // Text-printing program. 3 4 public class Welcome1 { 5 6 // main method begins execution of Java application 7 public static void main( String args[] ) 8 { 9 System.out.println( "Welcome to Java Programming!" ); 10 11 } // end method main 12 13 } // end class Welcome1

Welcome to Java Programming!

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A First Program in Java

Comments // remainder of line is comment

Comments ignored Document and describe code

Multiple line comments: /* ... */

1 // Fig. 2.1: Welcome1.java

/* This is a multiple line comment. It can be split over many lines */

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A First Program in Java

Class Declaration

Every Java program has at least one defined class

Keyword: words reserved for use by Javaclass keyword followed by class nameThe class name has to be an identifier

Naming Convention: capitalize every word Example: SampleClassName

4 public class Welcome1 {

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A First Program in Java

Body Delimiter Left brace {

Begins body of every class A corresponding right brace “}” ends definition

(line 13)

Indentation Convention Whenever you type an left brace “{“, immediately

type the right brace “}”. Then, indent to begin type the body.

4 public class Welcome1 {

13}/* End of Class Welcome1 */

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A First Program in Java

Program Entry Applications begin executing at main()

Exactly one method must be called main Parenthesis indicate main is a method Java applications contain one or more methods

Methods can perform tasks and return result void: means main returns no information args[]:input arguments in String data type.

5 public static void main( String args[] )

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A First Program in Java

Statements Statements are instructions to commend

hardware to perform some operations. It must end with semicolon “;”

System.out: standard output object System.out.println: displays line of text

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

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A First Program in Java

Execution Steps

Javacompiler

Javasource code byte-code

EXECUTION

JAVA PROGRAM EXECUTION

byte-codeinterpreter

JVM

Welcome.java

.class

javac Welcome.java

java Welcome

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A First Program in Java

Execution Steps Compiling a program

Open a command window, go to program’s directory.

Type javac Welcome.java If no errors, Welcome.class created

Executing a program Type java Welcome to start JVM and then run

the program Welcome.class Interpreter calls method main

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A First Program in Java

Demonstration 4 public class Welcome1 { 5 6 // main method begins execution of Java application 7 public static void main( String args[] ) 8 { 9 System.out.println( "Welcome to Java Programming!" ); 10 11 } // end method main 12 13 } // end class Welcome1

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Text Displaying

Displaying MethodsSystem.out.println

Prints argument, puts cursor on new lineSystem.out.print

Prints argument, keeps cursor on same lineSystem.out.printf

Prints argument which is a format string

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

7 System.out.print("Welcome to “);8 System.out.println(“Java Programming!" );

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Text Displaying

Escape Sequences The backslash “\” is called an escape

character to indicate a “special character” is to be output.

Backslash combined with character makes escape sequence.Escape Sequence Description

\n Newline\t Horizontal Tab\r Carriage Return. Position the cursor at the

beginning of the current line\\ Backslash\” Double Quote

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Text Displaying

Escape Sequences7 System.out.println("Welcome\nto\nJava\n

Programming!" );

WelcometoJavaProgramming!

7 System.out.println(“\”in quotes\”" );

“in quotes”

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Text Displaying

Format String The first argument of printf() is a format

string Fixed Text Format Specifier

Format specifier is a placeholder for a value and specifies the type of data. Percent Sign (“%”) Data Type

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Text Displaying

Format StringType Character

Input String Result

%c char character%d signed int signed decimal integer%f float real number, standard notation%s string string

7 System.out.printf(“%s\n%s\n”, “Welcome to”, “Java Programming!" );

Welcome toJava Programming!

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Value Input: Integer Addition

Requirements Read in two integers from users Compute the summation of them Print out the result on the screen

Enter first integer:1Enter second integer:3Sum is: 4

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Value Input: Integer Addition

Variable Declaration Every variable has a name, a type, a size and a value

Name corresponds to location in memory When new value is placed into a variable, replaces

(and destroys) previous value Reading them from memory does not change them

int number1=10;

int number1;number1=10;

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Value Input: Integer Addition

Variable Declarationpublic class Addition {

// main method begins execution of Java applicationpublic static void main( String args[] ){

int number1;int number2;int sum;…………

}/* End of main */

}/* End of class Addition */

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Value Input: Integer Addition

import java.util.Scanner;public class Addition {

// main method begins execution of Java applicationpublic static void main( String args[] ){

……// create Scanner to obtain input from command windowScanner input = new Scanner( System.in );// read the first integer System.out.print("Enter first integer:");number1 = input.nextInt();// read the second integerSystem.out.print("Enter second integer:");number2 = input.nextInt();……

}/* End of main */}/* End of class Addition */

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Value Input: Integer Addition

import java.util.Scanner;public class Addition {

// main method begins execution of Java applicationpublic static void main( String args[] ){

……sum = number1 + number2;System.out.printf("Sum is: %d\n", sum);}/* End of main */}/* End of class Addition */

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Arithmetic

Description Arithmetic calculations used in most

programs Asterisk ‘*’ indicates multiplication Percent sign ‘%’ is the remainder (modulus)

operator Integer division truncates remainder7 / 5 evaluates to 1

Modulus operator % returns the remainder 7 % 5 evaluates to 2

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Arithmetic

Operator precedence Some arithmetic operators act before

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

() Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.

*, /, or % Multiplication Division Modulus

Evaluated second. If there are several, they are evaluated left to right.

+ or - Addition Subtraction

Evaluated last. If there are several, they are evaluated left to right.

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Equality and Relational Operators

Description A condition is an expression that can be

either true or false. It is used in control statements (if, for,

while) to change the execution flow of program

Conditions can be formed by using Equality Operators Relational Operators

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Equality and Relational Operators

Equality/Relational OperatorsStandard Algebraic

Java Equality

Sample Meaning

= == x == y x is equal to y?!= x != y x is not equal to y ?

> > x > y x is greater than y ?< < x < y x is less than y?

>= x >= y x is greater than or equal to y

<= x <= y x is less than or equal to y

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Equality and Relational Operators

Exampleimport java.util.Scanner;public class Comparison {

public static void main( String args[] ){int number1=100;int number2=200;if(number1 == number2){System.out.printf(“%d == %d \n”, number1, number2);}/* End of if-condition */if(number1 != number2){System.out.printf(“%d != %d \n”, number1, number2);}/* End of if-condition */

}/* End of main */}/* End of class Addition */

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