java 1.4.2

Programming Java







Java Basics







Incheon Paik









1 Computer Industry Lab.

Java

Contents

 Background

 The Java Virtual Machine

 Applications & Applets

 Classes & Objects

 The 3 Principles of Object Oriented Programming

 Start up Java

 Variables & Assignments

 Strings & Characters

 Arithmetic Operators & Expressions

 Type Conversion

 Comments

 Arrays

 Keywords



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Background / History

 Sun Microsystems Inc.

 James Gosling





 1990, “Green Project”

 1991, Develop the Language for Household Products => To

General Developing Language



 Java

 James Gosling, Arthur Van Hoff, Andy Bechtolsheim



 Coffee Materials in Indonesia



 Write once, Run everywhere

 Spread Rapidly through WWW and Internet









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Byte Code and Java Virtual Machine

 Existing Development Environment





Binary

File



Compiler(Pentium) Pentium



Source Binary

Code File



Compiler(PowerPC) PowerPC





Binary

%cc Hello.c –o Hello File

% Hello Compiler(SPARC) SPARC



Run Binary Code





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Bytecodes and the Java Virtual Machine

 Java Development Environment





Java

Interpreter

Java Compiler

(Pentium) Pentium

Java Java

Java

Code ByteCode

Interpreter

(Independent on

Java Compiler Platform)

PowerPC

(PowerPC)

Java

%javac Hello.java Interpreter

Hello.class created



% java Hello Java Compiler SPARC

(SPARC)

Run JVM Byte Code

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Java

Java Program

 Java Application Program

 Application



 Program written in general programming



language



 Applet

 Program running in Web Browser Environment



 Can be viewed by appletviewer or Web browser



with JVM









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Classes and Objects

 Object

 Memory Space to Define State and Operation



 Instance of Class









 Class

 Template of Creating Object









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The 3 Principles of Object Oriented

Programming

 Encapsulation

 Control Access the data and method in program code



 Inheritance

 Inherit the data and methods of parent class



 Polymorphism



Shape getArea()

Shape Obj = new Ellipse();

Obj.getArea();





Ellipse Rectangle Triangle

Which Area?

getArea()

getArea() getArea()









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The Java Class Libraries

 java.applet : Applet related

 java.awt : Abstract Window Toolkit

 java.awt.event : Event process from awt component

 java.awt.image : Image processing

 java.beans : JavaBeans Component

 java.io : File or Network I/O Support

 java.lang : Java Language Support

 java.net : Network related functions

 java.util : Utility function









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Java 2 SDK

 Java 2 Software Development Kit (Java 2 SDK)

 Java Application or Applet Development and



Running Environment



 Java 2 Runtime Environment (JRE)

 Java Running Environment









 Java 2 Standard Edition

 Java 2 Micro Edition

 Java 2 Enterprise Edition







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Java

Start a Java Application

Java C

Class Name Main Function

“Hello.java” “hello.c”

Main method

class Hello { void main() {

public static void main(String args[]) { printf(“Hello World\n”);

System.out.println(“Hello World”); }

}









% javac Hello.java Compile % cc hello.c –o hello





Run

% java Hello % hello









Result Hello World





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Java

Variables and Assignments

 Variables

 Types

 char 16bits Unicode character data

 boolean Boolean Variable

 byte 8 bits signed integer

 short 16 bits signed integer

 int 32 bits signed integer

 long 64 bits signed integer

 float 32 bits signed floating point number

 double 64 bits signed floating point number







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Variables and Assignments

Variable Declaration

type varName; float x, y, x;



Value assignments

varName = value;



int num = 100;

long m = 21234234L

double type : .5 0.8 9e-2 -9.3e-5

float type : 1.5e-3f;







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Strings and Characters



 String : sequence of character

String s = “Enter an integer value: ” ;

Char c = „A‟; Unicode







 Concatenation Operator „+‟

String s = “Lincoln said: ” + “\” Four score and seven years ago\”” ;

Result :

Lincoln said: “Four score and seven years ago”









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Arithmetic Operators

 Operators

 + - * / %



 += -= *= /= %=

 ++ --



5/2  2 Why isn‟t it 2.5 ?

5%2  1

4/2  2

4%2  0

 count * num + 88 / val – 19 % count



 j += 6;  j = j + 6;









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Type Conversions in Expression

char ch; int i; float f; double outcome;

ch = „0‟; i = 10; f = 10.2f;

outcome = ch * i / f;

int

float

double double

Yes No





double float

Yes No



float long

Yes No





long int









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Type Conversions in Assignment

 Widening Conversion

byte b = 127;

int i;

i = b;

 Narrowing Conversion

byte b;

int i = 258;

b = (byte) i;

 Wrong Conversion

byte b;

int i = 127;

b = i;

 Right Conversion (But data may be lost)

byte b;

int i = 127;

b = (byte) i;



Type Casting





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Comments

 Single Line Comment

 int i = 10 ; // i is counter



 Multiple Line Comment

/*

Some comments

*/

 Documentation Comment

/**

Using “javadoc” Tool,

Documentation Comment make document



*/







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Arrays ( One Dimensional)



Definition of One Dimensional Array



type VarName[]

int ia[];





Assign Range to One Dimensional Array



varName = new type[size]

ia = new int[10];





Declaration of One Dimensional Array with Range



type varName[] = new type[size]

int ia[] = new int[10];









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Arrays ( One Dimensional)



Number of elements in Array



varName.length







Initialization of One Dimensional Array



Type varName[] = {e0, … , en};

int j[] = {0, 1, 2, 3, 4, 5};

int k[];

K = j;









Example 1.15







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Arrays ( Multi-Dimensional)



Definition of Two Dimensional Array



type VarName[][];

float fa[][];





Assign Range to Two Dimensional Array



varName = new type[size1][size2];

fa = new float[2][3];





Declaration of Two Dimensional Array with Range



type varName[][] = new type[size1][size2];

float fa[] = new float[2][3];









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Java

Arrays ( Two Dimensional)



Number of elements in Multi-Dimensional Array



varName.length Number of Raw









Number of elements in Each elements of Multi-Dimensional Array



varName[index].length







Initialization of Multi-Dimensional Array



Type varName[][] = {{e00, … , e0n}, {e10,…,e1y}, {e20, …, e2z}};







Example 1.16







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Java Keywords



 50 Java Keywords

abstract double int super

boolean else interface switch

break extends long synchronized

byte final native this

case finally new throw

catch float package throws

char for private transient*

class goto* protected try

const* if public void

continue implements return volatile

default import short while

do instanceof static strictfp

assert (New in 1.5) enum (New in 1.5)

The “assert” is recognized as keyword in JDK1.4 compiler, but we could not use it.

It can be used it from 1.5.





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Java

Exercise

 Step 1

 Refer to this lecture (slide #11)



 Step 2 (How to make & run Applet)

 (1) Make Applet Program

import java.awt.Graphics;

public class HelloWorldApplet extends java.applet.Applet {

public void paint (Graphics g) {

g.drawString(“Hello World!”,5,25); }

} // end of Applet

 (2) Compile(using javac) to create HelloWorldApplet.class

 (3) Create HTML file (ex; HelloWorld.html) to include applet



 (4) Run Applet using Appletviewer or Applet enabling Web browser

% appletviewer HelloWorld.html









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Exercise

 Step 3 (Type Conversion)

 Refer to this lecture (slides #16,17)



 Step 4 (Array)

 Refer to this lecture (slide #22)









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