Download Basic Java Seminar 2/2

Seminars on 4th SPARCS Exhibition - The second one
Basic Java Seminar 2/2
Novemberr 5, 1997
SPARCS
Nam Sedong
dgtgrade@sparcs.kaist.ac.kr
What is Java?
• A way to make Web pages sexy?
• A language like C++, Smalltalk?
• Computing Platform
– Java Programming Language
– Java (Virtual) Machine (JVM)
– Java API (Application Programmers’ Interface)
• MFC
Java Language
• C++ -- +++
– Object Oriented
– no multiple inheritance
– no operator
overloading
– No pointer
• Secure
• Thread-safe
• Exception Handling
• Architecture Neutral
• Internationalization
– Unicode, 2 byte char
• Garbage Collection
• Standardization
– sizeof( int )
• Packages
• Network Oriented
– Class loading
Java Virtual Machine
• The engine that actually executes a Java
program
• key to many of Java’s features
– portability (Write once, run anywhere)
– efficiency
– security (Sandbox)
• virtual processor, virtual memory…
• Used in JDK, JRE, browsers
Java API
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package java.awt
package java.awt.datatransfer
package java.awt.event
package java.awt.image
package java.beans
package java.io
package java.lang
package java.lang.reflect
package java.math
package java.net
package java.rmi
package java.rmi.dgc
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package java.rmi.registry
package java.rmi.server
package java.security
package java.security.acl
package java.security.interfaces
package java.sql
package java.text
package java.util
package java.util.zip
Application & Applets
• Application
– standalone programs
– HotJava browser
• Applet
– a Java program to be included in HTML pages
and executed in a Java-compatible browser.
How Applet Run?
Compile
Java Source Code
Java Class File
Network
Web Browser
Before You go on
• JDK(Java Development Kit)
• Java-compatible browser
• References
– Java Tutorial HTML format
– Java API Documentation
• You can find many resources about Java at
http://www.javasoft.com
Hello World Application
/**
* The HelloWorldApp class implements an application that
* simply displays "Hello World!" to the standard output.
*/
class HelloWorldApp {
public static void main(String[] args) {
System.out.println("Hello World!"); //Display the string.
}
}
Compiling
• JDK:
– UNIX:
• javac HelloWorld.java
– DOS shell (Windows 95/NT):
• javac HelloWorld.java
• Other Visual Development Tools:
– Maybe, you can find “Compile” button, or etc.
• Output: HelloWorld.class
Running
• Run the program using the Java interpreter.
• JDK
– java HelloWorldApp
• Other Visual Development Tools:
– Maybe, you can find “Compile” button, or etc.
Variables and Data Types
• Primitive Type
– char
• 2byte, UNICODE
– boolean
• true or false
• Reference Type
• C data types Not supported
– pointer, struct, union
Class java.lang.String
String a = new String( “abc” );
String b;
b = new String( “def” );
String c = “abc”;
System.out.println( a.length( ) );
System.out.println( a.substring( 5, 10 ) );
System.out.println( a + b );
System.out.println( a == “abc” );
System.out.println( a.equals( “abc” ) );
System.out.println( c == “abc” );
String d = “This is”.concat( “String” );
Class java.lang.Math
int a;
a = Math.max( -5, -10 );
a = Math.abs( a );
int pi = Math.PI;
a = ( int )Math.max( -9.0, -10.2 );
java.util.Vector
Vector()
Vector(int)
Vector(int, int)
addElement(Object)
capacity()
contains(Object)
copyInto(Object[])
elementAt(int)
elements()
firstElement()
indexOf(Object) ...
Class java.util.Stack
public class Stack extends Vector {
public Object push(Object item);
public Object pop() throws EmptyStackException;
public Object peek() throws EmptyStackException;
public boolean empty();
public int search(Object o);
}
Abstract Window Toolkit(AWT)
• GUI, Look and Feel
• Components
– Button, Frame, Panel, TextField, ...
• Event Handling
– MouseListener, ComponentListener, ...
• Layout
– GridLayout, FlowLayout, …
AWT Component Hierarchy
HelloSPARCS Application
• A button turn in to red when pressed
– Add components to a container
– Add a listener to a component
– Multiple class in a file
HelloSPARCS.java 1/3
import java.awt.*;
import java.awt.event.*;
public class HelloSPARCS {
public static void main( String[] args ) {
Frame f = new Frame( "HelloSPARCS" );
f.add( new SPARCSButton( ) );
f.pack();
f.show();
}
}
Hello SPARCS.java 2/3
class SPARCSButton extends Button {
public SPARCSButton( ) {
this.setLabel( "SPARCS" );
this.addMouseListener( new SPARCSButtonAdapter( ) );
}
public SPARCSButton( Color argC ) {
this.setBackground( argC );
this.addMouseListener( new SPARCSButtonAdapter( ) );
}
}
Hello SPARCS.java 3/3
class SPARCSButtonAdapter extends MouseAdapter {
public void mouseClicked( MouseEvent argME ) {
if ( argME.getSource( ) instanceof SPARCSButton ) {
( ( SPARCSButton )argME.getSource( ) ).setBackground( Color.
red );
}
else {
System.err.println( "ERROR: ... " );
}
}
}
Hello World Applet
import java.applet.Applet;
import java.awt.Graphics;
public class HelloWorld extends Applet {
public void paint(Graphics g) {
g.drawString("Hello world!", 50, 25);
}
}
Class java.awt.Graphics
• Various devices, as well as onto off-screen
images.
• Component.getGraphics( )
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origin
clip
color
font.
XOR
repaint( )
• Another Thread for AWT
• repaint( )
– may not be called
– final state
• update( Graphics g)
• paint( Graphics g)
HW.html(Calling an Applet)
<HTML>
<HEAD>
<TITLE>
A Simple Program
</TITLE>
</HEAD>
<BODY>
<APPLET CODE="HelloWorld.class" WIDTH=150 HEIGHT=25>
</APPLET>
</BODY>
</HTML>
The Life Cycle of an Applet
public class Simple extends Applet {
...
public void init() { . . . }
public void start() { . . . }
public void stop() { . . . }
public void destroy() { . . . }
...
}
한글? Unicode?
• char
– 2byte
• String
• Unicode 2.0
– 2 byte
• 한글로 된 변수이름을 쓸 수 있다.
Java의 미래?
• Today, 5 times slower than C++
– Just In-Time(JIT) compiler
– JAR
• Write Once, Run Anywhere?
– Java Foundation Class
• Assembly  C
• JavaBeans - Software Component
• JavaStation - (Not Virtual)Machine
References
• http://www.javasoft.com/docs/books/tutorial/index.html
• http://www.javasoft.com/products/jdk/1.1/docs/api/packages.htm
l
• http://www.javasoft.com/docs/books/jls/html/index.html
• 전문가로 큰다, 김도형(dynaxis), 마이크로소프트웨어
• Java Unleashed, Sams net
• Java Virtual Machine, Jon Meyer&Troy Downing, O’Reilly
Contact Information
• dgtgrade@sparcs.kaist.ac.kr
• dgtgrad@ara.kaist.ac.kr
• dgtgrade@csqueen.kaist.ac.kr
• dgtgrade@noah.kaist.ac.kr
• dgtgrade@neowiz.com
• Office: 869-5400
• Off-line: SPARCS room