Java - Trang ď Chap01

„ James Gosling „ 1990, “Green Project” „ 1991, Develop the Language for Household Products => To General Developing Language „ Java „ J ames Gosling, A rthur V an Hoff, A ndy Bechtols

Programming Java

Java Basics

Incheon Paik

Contents

„ Applications & Applets

„ Classes & Objects

„ Strings & Characters

Background / History

„ Sun Microsystems Inc.

„ James Gosling

„ 1990, “Green Project”

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

General Developing Language

„ Java

„ J ames Gosling, A rthur V an Hoff, A ndy Bechtolsheim

„ Coffee Materials in Indonesia

„ Write once, Run everywhere

„ Spread Rapidly through WWW and Internet

Byte Code and Java Virtual Machine

„ Existing Development Environment

Source

Code

Compiler(Pentium)

Compiler(PowerPC)

Compiler(SPARC)

Binary File Pentium

PowerPC

SPARC

Binary File

Binary File

%cc Hello.c –o Hello

% Hello

„ Java Development Environment

Java Compiler (Pentium)

Java Compiler (PowerPC)

Java Compiler (SPARC)

Java Interpreter Pentium

PowerPC

SPARC

Java Interpreter

Java Interpreter

Java

Code

Java ByteCode

(Independent on Platform)

%javac Hello.java

Hello.class created

% java Hello

Byte Code Run JVM

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

Classes and Objects

„ Object

„ Memory Space to Define State and Operation

„ Instance of Class

„ Class

„ Template of Creating Object

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

Ellipse Rectangle Triangle

getArea()

getArea() getArea() getArea()

Shape Obj = new Ellipse(); Obj.getArea();

Which Area?

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

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

Start a Java Application

“Hello.java”

class Hello {

public static void main(String args[]) {

System.out.println(“Hello World”);

}

% javac Hello.java

% java Hello

Compile Run

“hello.c”

void main() { printf(“Hello World¥n”);

}

% cc hello.c –o hello

% hello

Hello World

Result

Class Name Main method

Main Function

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

Variables and Assignments

int num = 100;

long m = 21234234L

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

float type : 1.5e-3f;

Variable Declaration

type varName;

Value assignments

varName = value;

float x, y, x;

Strings and Characters

„ String : sequence of character

String s = “Enter an integer value: ” ;

Char c = ‘A’;

„ Concatenation Operator ‘+’

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

Result :

Lincoln said: “Four score and seven years ago”

Unicode

Arithmetic Operators

„ Operators

„ + - * / %

„ += -= *= /= %=

„ ++

5 / 2 Æ 2 Why isn’t it 2.5 ?

5 % 2 Æ 1

4 / 2 Æ 2

4 % 2 Æ 0

„ count * num + 88 / val – 19 % count

„ j += 6; Î j = j + 6;

Type Conversions in Expression

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

ch = ‘0’; i = 10; f = 10.2f;

outcome = ch * i / f;

double

double float

int

float

double

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

Comments

„ Single Line Comment

„ int i = 10 ; // i is counter

„ Multiple Line Comment

/*

Some comments

*/

„ Documentation Comment

/**

Documentation Comment

*/

Using “javadoc” Tool, make document

Arrays ( One Dimensional)

type VarName[]

Definition of One Dimensional Array

int ia[];

varName = new type[size]

Assign Range to One Dimensional Array

ia = new int[10];

type varName[] = new type[size]

Declaration of One Dimensional Array with Range

int ia[] = new int[10];

Arrays ( One Dimensional)

varName.length

Number of elements in Array

Type varName[] = {e0, …, en};

Initialization of One Dimensional Array

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

int k[];

K = j;

Example 1.15

Arrays ( Multi-Dimensional)

type VarName[][];

Definition of Two Dimensional Array

float fa[][];

varName = new type[size1][size2];

Assign Range to Two Dimensional Array

fa = new float[2][3];

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

Declaration of Two Dimensional Array with Range

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

varName.length

Number of elements in Multi-Dimensional Array

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

Initialization of Multi-Dimensional Array

Example 1.16

varName[index].length

Number of elements in Each elements of Multi-Dimensional Array

Number of Raw

Java Keywords

„ 50 Java Keywords

continue implements return volatile

do instanceof static strictfp

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

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

It can be used it from 1.5.

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

<applet code="HelloWorldApplet.class" width="150" height="25">

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

% appletviewer HelloWorld.html

Exercise

„ Step 3 (Type Conversion)

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

„ Step 4 (Array)

„ Refer to this lecture (slide #22)