Principles of Object-Oriented Software Development The language Java

Introduction Terminology Expressions Control Objects Inheritance Techniques Summary

Java -- the dial-tone of the Internet 1995 Introduction at WWW with AWT x with modified event handling 1998 version 1.2 (beta) with Swing Design principles -- safety a modern programming language,C++ syntax, no pointers virtual machine (runs on many platforms) libraries: threads, networking, AWT downloadable classes, support for applets extensions and APIs: Beans, Swing, MEDIA, 3D See: and

Keywords: new, finalize, extends, implements, synchronized Java overview Language features: no pointers -- references only simplify life garbage collection -- no programmers' intervention constructors -- to create and initialize single inheritance -- for refinement interfaces -- abstract classes synchronized -- to prevent concurrent invocation private, protected, public -- for access protection

Type expressions basic types -- int, char, float,... Array -- int ar[SIZE] String -- String[] args class -- user-defined

Expressions operators -- +, -,.., <, <=,.., ==, ! =,.., &&, || indexing -- o[ e ] access -- o.m(...) in/decrement -- o++, o-- conditional -- b?e1:e2 Assignment var = expression modifying -- +=. -=,...

Control conditional -- if (b) S1; else S2; selection -- switch(n) { case n1: S1; break;... default:... } iteration -- while (b) S looping -- for( int i = 1; i <= MAX; i++) S jumps -- return, break, continue Java -- control

Hello World -- Java (1) public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World"); } };

Hello World - interface public interface World { public void hello(); }; Hello World - class public class HelloWorld implements World { public void hello() { System.out.println("Hello World"); } }; Java -- objects (2)

Hello World -- Java (2) import java.awt.Graphics; public class HelloWorld extends java.applet.Applet { public void init() { resize(150,50); } public void paint(Graphics g) { g.drawString("Hello, World!", 50, 25); } }; Java -- inheritance

Java -- techniques applets -- extend your browser servlets -- extend your server networking -- urls, sockets RMI -- remote method invocation reflection -- meta-information beans -- component technology JNI -- writing native methods javadoc -- online class documentation

The language Java design principles -- safety terminology -- object, interface syntax -- like C++ objects -- abstract data types, interfaces inheritance -- single inheritance techniques -- dynamic casts, reflection, APIs