Internetandjava

Internet and Java Foundations, Programming and Practice Rajkumar Buyya School of Computer Science and Software Engineering Monash University Melbourne, Australia Email: rajkumar@dgs.monash.edu.au URL: http://www.dgs.monash.edu.au/~rajkumar

Agenda Internet and its Evolution Internet Tools Web and its Programming Java for Internet Programming Java Nuts and Bolts Java Platform Developing Applets and Applications Challenges and Future Directions

What is the Internet ? It is a global network of computers that communicate with each other using a variety of protocols and overcoming various communication barriers. It is like International Telephone System

Internet Technology Evolution Internet is much bigger than what we think More than 25 years old More than doubling every year Technology effect suddenly every body sees the need for a technology like the radio or the TV 10 terabytes flows everyday

Internet Use of internet advertisement/elections/newspapers information is public Ubiquitous technology Network is the computer Intranets - internal TCP/IP nets PC accounts for 55% of total IT Applications tied to platform - API lock-in

Internet Evolution File & mail TCP/IP Webpages Netscape On line connects to internet Secure payments Multi media Authoring Java VRML HTML Internet everywhere Internet appliances Price based services Live communities ? ? ? ? ? ? ? 10% of Market 20% of Market Total Market

Early Internet Early Internet supported only email . File Transfer Protocol development - ftp sites. Network News was added to the Internet. Archie - A program to canvass anonymous ftp sites and create a database of what is available Gopher- A menu-driven interface used to search for information. Archie and Gopher could answer questions only like ‘what FTP server contains info about “xxxx” ‘

World Wide Web World Wide Web conceptualized by Tim Berners-Lee at CERN in Switzerland Concept of Hypertext led to the development of the Hypertext Markup Language (HTML) Tim Berners-Lee proposed the ‘Browser’ program Scientists at CERN designed a TCP/IP based protocol to share Hypertext information called HTTP. WWW officially is described as a” Wide-area hypermedia information retrieval initiative aiming to give universal access to a large universe of documents.

HTML Hypertext -A little Hype and a Little Text. Hypertext point to information which can be local or remotely located. HTML -Derivative of the SGML( Standard Generalized Markup Language). HTML -information , commands for the Browser for formatting documents. HTML -The de-facto language for publishing on the Internet. Hypermedia- Hyper-links to Multimedia .

Internet Tools Browsers- A tool used to view documents on the WWW Web servers - Machines which run the HTTP-server Software that respond to HTTP requests which it receives Authoring Tools - Editors specially made for editing HTML documents Filters -Tools to convert legacy documents to HTML format Scripting -Languages used for scripting WAIS- Wide Area Information Servers (WAIS) for indexing and doing full text searches

How does the Web work ? Web -Designed around Client/Server Architecture Web Clients ( Web Browsers ) -send requests for documents to any Web Server Web Server -Program that responds to HTTP requests Hyperlink Web client connects to the specified Web Server The server responds by sending the information asked for The Browser formats the received HTML data and displays it

How does the Web Work HTTP Send the “INFORMATION ABOUT C-DAC ACTS” The information about C-DAC ACTS The client sends an HTTP message to a computer running a Web Server program and asks for a document The web server sends the hypermedia HTML documents to the client. You end up seeing the document on your screen

HTML document <HTML> <TITLE>Centre for Development of Advanced Computing </TITLE> <BODY BGCOLOR=“#E7CCCC” TEXT=“#000000” LINK=“#0000FF”> ... ... <A HREF=“mailto:webmaster@cdacb.ernet.in> webmaster</A> </BODY> </HTML>

URLs URLs- The Hypertext links we use today are known as Universal Resource Locator URLs-Each name is unique across the Internet An URL looks like this http://system.domain.ext:999/dir1/dir2/dir3/file.html?blue# Parts of a URL are, Service type, System Name, Port, Directory path, Filename,Search Components or Variables Service type, System Name, Directory path are the required parts of the URL

CGI (Common Gateway Interface) CGI makes the Web a Two-way interface CGI -lets the user run a script when a web page is accessed Information from the Web Client is received through simple ‘fill-in-the-forms’ kind of interface FORMS - Integrates data sheets, menus , check boxes CGI makes the Web interactive CGI -complicated to setup ,requires PERL knowledge HTML books talk less about CGI

Authoring tools and Filters Authoring tools- Editors for HTML documents Editors similar to WYSIWYG word processing programs Semi-WYSIWYG or completely WYSIWYG Provide syntax checking and correction Filters -Convert legacy documents to HTML format Filters are useful when the documents already exist Authoring tools- HoTMetaL, HTML Assistant -Shareware

Preconfigured v/s Integrated Internet Products Integrated Internet Products- From multiple vendors Preconfigured Systems- Web Server and a Client ready to use Sun’s Netra Internet Server SGI’s WebFORCE Indy and WebFORCE Challenge S Apple’s Internet Server Solution DEC’s Internet AlphaServer Integraph’s Web Server 10

Future Directions Additions to HTML (Grammar, Maths, Display control) VRML (Virtual Reality Markup Language) Security - Using Scrambling and Encryption Common Client Interface (CCI)- Allows Clients to pass information back and forth between the Browser and the External Viewer Charge Mechanisms Performance Enhancements- Sending a page and graphics for that page in one connection

Interesting URLs http://www.whitehouse.gov ( The WhiteHouse) http://www.w3.org (Everything about the WWW) http://sunsite.unc.edu (Software on Sun) http://www.indnet.org (India Net Foundation Services) telnet://www.arbornet.org (Free Public Access Unix System) http://www.infoseek.com (Search engines, Add URL ) http://www.infophil.com (World Alumni on the net) http://www.rocketmail.com (Free Email ) http://members.tripod.com (Free Website,2MB space) http://www.bangaloreonline.com (Offers virtual web servvices for compinies to host their website). http://www.prajavani.com (Kannada news paper on web)

API Bottleneck Network LAN LAN PC SUN MAC Server

The OS - Platform lock Application Application Application OS Applications tied to OS OS tied to Platform Application Application

The Web Application Application Application Application BROWSER OS OS OS OS * Seeded by HTML from CERN * Revolutionised by MOSAIC * Standardised, universal interface to data * Graphical * Broadcast capability - publish once, reach millions Application

Making life easier! Data on the web Browser platform independent Click on application - run on any machine Java the programming language of the 21 century

Java - An Introduction Java - The new programming language from Sun Microsystems Java -Allows anyone to publish a web page with Java code in it Java - CPU Independent language Created for consumer electronics Java - James , Arthur Van , and others Java -The name that survived a patent search Oak -The predecessor of Java Java is “C++ -- ++ “

Java From 10,000 Ft. According to the world, Java is... According to Sun, Java is... On closer inspection, Java is

According to the World, Java Is... Snazzy Web pages The cross-platform language we want The rest-of-the-worlds answer to Bill The C++ replacement we need The C++ replacement we dont need A bunch of hype

According to Sun, Java is... Simple and Powerful Object Oriented Portable Architecture Neutral Distributed Multi-threaded Robust, Secure/Safe Interpreted High Performance Dynamic pogramming language/platform. Buzzword compliant!

On Closer Inspection, Java is... Simple Pure Portable Surprisingly effective

As a whole, Java is a Comprehensive Programming Solution Object Oriented Portable High Performance Geared for Distributed Environments Secure

Java as Object Oriented “ Objects all the way down” Simple and Familiar: “C++ Lite” No Pointers! Garbage Collector Dynamic Binding Single Inheritance with “Interfaces”

Java as Portable Unlike other language compilers, Java complier generates code (byte codes) for Universal Machine. Java Virtual Machine (JVM): Interprets bytecodes at runtime Architecture Neutral No Link Phase Higher Level Portable Features: AWT, Unicode

Total Platform Independence JAVA COMPILER JAVA BYTE CODE JAVA INTERPRETER Windows 95 Macintosh Solaris Windows NT (translator) (same for all platforms) (one for each different system)

Architecture Neutral & Portable Java Compiler -Java source code to bytecode Bytecode - an intermediate form, closer to machine representation A virtual machine on any target platform interprets the bytecode Porting the java system to any new platform involves writing an interpreter that supports the Java Virtual Machine The interpreter will figure out what the equivalent machine dependent code to run

Java as High Performance JVM uses “lean and mean” bytecodes Small binary class filtes Just-in-time Compilers Multithreading Native Methods

Java in the World of Distributed Computing Class Loader Lightweight Binary Class Files Multithreading Dynamic Good communication constructs Secure

Java as Secure Language designed as safe Strict compiler Dynamic Runtime Loading (Verifier) Runtime Security Manager

Object Oriented Languages -a Comparison Feature C++ Objective C Ada Java Encapsulation Yes Yes Yes Yes Inheritance Yes Yes No Yes Multiple Inherit. Yes Yes No No Polymorphism Yes Yes Yes Yes Binding (Early/Late) Both Both Early Late Concurrency Poor Poor Difficult Yes Garbage Collection No Yes No Yes Genericity Yes No Yes No Class Libraries Yes Yes Limited Yes

Java better than C++ ? No Typedefs, Defines, or Preprocessor No Global Variables No Goto statements No Pointers No Unsafe Structures No Multiple Inheritance No Operator Overloading No Automatic Coercions No Fragile Data Types ?

Basic Data Types Types boolean either true of false char 16 bit Unicode 1.1 byte 8-bit integer (signed) short 16-bit integer (signed) int 32-bit integer (signed) long 64-bit integer (singed) float 32-bit floating point (IEEE 754-1985) double 64-bit floating point (IEEE 754-1985) String (class for manipulating strings) Java uses Unicode to represent characters internally

Java Integrates Power of Compiled Languages and Flexibility of Interpreted Languages

Two Types of JavaApplications Different ways to write/run a Java codes are: Application - A stand-alone program that can be invoked from command line . A program that has a “ main ” method Applet - A program embedded in a web page , to be run when the page is browsed . A program that contains no “main” method Application -Java interpreter Applets - Java enabled web browser (Linked to HTML via <APPLET> tag. in html file)

Java Bytecodes move locally or through network Java Source (.java) Java Compiler Java Bytecode (.class ) Runtime System Class Loader Bytecode Verifier Java Class Libraries Operating System Hardware Java Virtual machine Runtime Environment Compile-time Environment Java Environment/ Life Cycle of Java Code Java Interpreter Just in Time Compiler

Java Development Kit javac - The Java Compiler java - The Java Interpreter jdb- The Java Debugger appletviewer -Tool to run the applets javap - to print the Java bytecodes javaprof - Java profiler javadoc - documentation generator javah - creates C header files

Hello Internet // hello.java: Hello Internet program class HelloInternet { public static void main(String args[]) { System.out.println(“Hello Internet”); } }

Program Processing Compilation # javac hello.java results in HelloInternet.class Execution # java HelloInternet Hello Internet #

Simple Java Applet // HelloWorld.java: A sample applet import java.applet.Applet; public class HelloWorld extends Applet { public void paint(Graphics g) { g.drawString(“Hello World !”,25,25); } }

Calling an Applet <HTML> <TITLE> Hello Worls Applet </TITLE> <APPLET code=“HelloWorld.class” width=500 height=500> </APPLET> </HTML>

Execution of Applets Hello Hello Java <app= “ Hello”> 4 APPLET Development “hello.java” AT CDAC-India The Internet hello.class AT C-DAC’S WEB SERVER 2 3 1 5 Create Applet tag in HTML document Accessing from CRAY Corp. (USA) The browser creates a new window and a new thread and then runs the code

Web Perspective How did Web interactions work? How do they work with Java? Distributed Java objects and the Web

Significance of downloading Applets Interactive WWW Flashy animation instead of static web pages Applets react to users input and dynamically change Display of dynamic data WWW with Java - more than a document publishing medium http://www.javasoft.com/applets/alpha/applets/StockDemo/standalone.html

Power of Java and the Web Deliver applications, not just information Eliminate porting Eliminate end-user installation Slash software distribution costs Reach millions of customers - instantly

Bytecode Verifier Called when class is first loaded in runtime environment Verifies bytecodes meet certain set of properties Verifier uses Theorem Prover Verified code runs faster After verification, interpreter defines memory layout

Class Loader Unique “Namespace” for each origin Local namespace classes are called “built-ins” Prevents class “spoofing”

Security Manager Prevents unauthorized disk read/writes Restricts network access Other access restrictions (native methods) Implementation is browser dependent

General Language Features C/C++ like syntax No pointers Objects all the way down Objects request services of other objects through messages Messages result in invocation of class methods

Removed From C++ Operator overloading Pointers and Array/pointers Multiple-inheritance of implementation Enum, typedef, #define Copy constructors, destructors Templates And other stuff....

Added or Improved over C++ Interfaces: type Vs. class Garbage collection Exceptions (More powerful than C++) Strings Instanceof Package Multi-threads

Rich Object Environment Core Classes language Utilities Input/Output Low-Level Networking Abstract Graphical User Interface Internet Classes TCP/IP Networking WWW and HTML Distributed Programs

Main Packages java.lang java.util java.io java.awt java.awt.image java.applet java.net

Java Fundamentals Constructs Graphics Multithreading Streams and Networking Networking

Unit I--Java Constructs what is Java, basic constructs, including classes and objects constructors, this and super keywords, inheritance, abstract classes, interfaces, inner classes, exceptions.

Unit II--Graphics Programming How to build Graphical User Interfaces in Java: GUI components, event handling, layout management.

Unit III--Advanced Features Applets, Threads, Streams I/O, Networking

Unit I -- What is Java ? A programming language: Object oriented (no friends, all functions are members of classes, no function libraries -- just class libraries) simple (no pointer arithmetic, no need for programmer to deallocate memory) platform independent dynamic interpreted

Types Eight basic types 4 integers ( byte, short, int, short ) [ int a; ] 2 floating point ( float, double ) [ double a;] 1 character ( char ) [ char a; ] 1 boolean ( boolean ) [ boolean a; ] Everything else is an object String s;

Classes and objects declaring a class class MyClass { member variables; … member functions () ; … } // end class MyClass

Java programs Two kinds Applications have main() run from the OS prompt Applets have init(), start(), stop(), paint(), update(), repaint(), destroy() run from within a web page

The first Java Application class MyApp { public static void main(String s [ ] ) { System.out.println(“Hello World”); } } // end class MyApp

Declaring and creating objects declare a reference String s; create/define an object s = new String (“India”); India

Arrays (are objects in Java) declare int a [ ] ; // 1-dim int [ ] b ; // 1-dim int [ ] c [ ]; // 2-dim int c [ ][]; // 2-dim allocate space a = new int [7]; c = new int [7][11];

Arrays have length used to retrieve the size of an array int a [ ] = new int [7]; // 1-dim System.out.println(a.length); will print ‘7’ int b [ ] [ ] = new int [7] [11]; System.out.println(a.length); will print ‘7’ System.out.println(b.length * b[0].length); will print ‘77’

… this is because Let int [][][][] array = new int [7][11][10][21] , then … array.length * array[3].length * array[3][5].length * array[3][5][2].length is 7 x 11 x 10 x 21

Constructors All objects are created through constructors They are invoked automatically class Weight { int lb; int oz; public Weight (int a, int b ) { lb = a; oz = b; } }

this keyword refers to “this” object (object in which it is used) usage: with an instance variable or method of “this” class as a function inside a constructor of “this” class as “this” object, when passed as parameter

this :: with a variable refers to “this” object’s data member class Weight { int lb ; int oz ; public Weight (int lb, int oz ) { this.lb = lb; this.oz = oz; } }

this :: with a method refers to another method of “this” class class Weight { public int m1 (int a) { int x = this.m2 (a); return x; } public int m2 (int b) { return b*7 ; } }

this :: as a function inside a constructor of “this” class must be used with a constructor class Weight { int lb, oz; public Weight (int a, int b) { lb = a; oz = b; } } public Weight (int x) { this( x, 0) ; } } Constructor is also overloaded (Java allows overloading of all methods, including constructors)

this :: as “this” object, when passed as parameter refers to the object that used to call the calling method class MyApp { int a; public static void main(String [] s ) { ( new MyApp() ).myMethod(); } public void myMethod() { yourMethod( this ); } public void yourMethod(MyApp inMyApp) { inMyApp .a = 77; } }

static keyword means “global”--all all objects refer to the same storage. applies to variables or methods” usage: with an instance variable of a class with a method of a class

static keyword (with variables) class PurchaseOrder { private static int POCount; // var. ‘a’ is shared by all objects of this class public static void main(String [] s ) { PurchaseOrder po1 = new PurchaseOrder(); po1.updatePOCount(); } public void updatePOCount() { POCount++; } }

static keyword (w/ methods) class Math { public static double sqrt(double x) { // calculate return result; } } class MyApp { public static void main(String [] s ) { double dd; dd = Math.sqrt(7.11); } }

Inheritance (subclassing) class Employee { protected String name; protected double salary; public void raise(double dd) { salary += salary * dd/100; } public Employee ( … ) { … } }

Manager can be made a sub/derived-class of Employee class Manager extends Employee { private double bonus; public void setBonus(double bb) { bonus = salary * bb/100; } public Manager ( … ) { … } }

Overriding (methods) class Manager extends Employee { private double bonus; public void setBonus(double bb) { …} public void raise(double dd) { salary += salary * dd/100 + bonus; } public Manager ( … ) { … } }

class First { public First() { System.out.println(“ First class “); } } public class Second extends First { public Second() { System.out.println(“Second class”); } } public class Third extends Second { public Third() {System.out.println(“Third class”);} } Inheritance and Constructors First class Second class Third class Topmost class constructor is invoked first (like us …grandparent-->parent-->child->)

access modifiers private same class only public everywhere protected same class, same package, any subclass (default) same class, same package

super keyword refers to the superclass (base class) usage: with a variable or method (most common with a method) as a function inside a constructor of the subclass

super :: with a method class Manager extends Employee { private double bonus; public void setBonus(double bb) { …} public void raise(double dd) { //overrides raise() of Employee super.raise(dd); // call Employee’s raise() salary += bonus; } public Manager ( … ) { … } }

super :: as a function inside a constructor of the subclass class Manager extends Employee { private double bonus; public void setBonus(double bb) { …} public Manager ( String name, double salary, double bonus ) { super(name, salary); this.bonus = bonus; } }

final keyword means “constant” applies to variables (makes a var. constant), or methods (makes a method non-overridable ), or classes (makes a class non-subclassable means “objects cannot be created” ).

final keyword with a variable class Math { public final double pi = 3.1412; public static double method(double x) { double x = pi * pi; } } note: variable pi is made “read-only”

final keyword with a method class Employee { protected String name; protected double salary; public final void raise(double dd) { salary += salary * dd/100; } public Employee ( … ) { … } } then: cannot ovveride method raise() inside the Manager class

final keyword with a class final class Employee { protected String name; protected double salary; public void raise(double dd) { salary += salary * dd/100; } public Employee ( … ) { … } } then: cannot create class Manager as a subclass of class Employee ( all are equal)

abstract classes and interfaces abstract classes may have both implemented and non-implemented methods interfaces have only non-implemented methods (concrete classes) have all their methods implemented

sample abstract class abstract class TwoDimensionalGeoFigure { public abstract double area(); public abstract double perimeter(); public abstract void printInfo(); public void setOutlineColor(Color cc) { // code to set the color } public void setInsideColor(Color cc) { // code to set the color } }

sample interface interface ResponceToMouseClick { public void mouseDown(); public void mouseUp(); public void mouseDoubleClick(); } class ConcreteMouseClick implements ResponseToMouse Click { // all above methods implemented here }

Exceptions (error handling) code without exceptions : ... int a = 7, b = 0, result; if ( b != 0) { result = a/b; } else { System.out.println(“b is zero”); } ... code with exceptions : ... int a = 7, b = 0, result; try { result = a/b; } catch (ArithmeticException e ) { System.out.println(“b is zero”); } ... A nice way to handle errors in Java programs

Exceptions (cont’d) ... int a = 7, b = 0, result; try { result = a/b; /// more code .. reading from a file } catch (ArithmeticException e ) { System.out.println(“b is zero”); } catch (IOException e ) { System.out.println(“Can’t read”); } finally { Sysytem.out.println(“Closing file”); /// code to close file } ...

methods throwing exceptions public int divide (int x, int y ) throws ArithmeticException { if (y == 0 ) { throw new ArithmeticException(); } else { return a/b ; } } // end divide()

Defining your own exceptions public int divide (int x, int y ) throws MyException { if (y == 0 ) { throw new MyException(); } else { return a/b ; } } // end divide() class MyException extends ArithmeticException {}frm

GUI Programming in Java (AWT and Event Handling)

AWT - Abstract Windowing Toolkit Single Windowing Interface on Multiple Platforms Supports functions common to all window systems Uses Underlying Native Window system AWT provides GUI widgets Event Handling Containers for widgets Layout managers Graphic operations

AWT - Abstract Window Toolkit Portable GUI - preserves native look & feel Standard GUI Components (buttons…) Containers - Panels, Frames, Dialogs Graphics class for custom drawing Layouts responsible for actual positioning of components: BorderLayout, GridLayout, FlowLayout, null layoit

Adding Components via Layouts setLayout(new BorderLayout()); // Add text field to top add("North",new TextField()); // Create the panel with buttons at the bottom... Panel p = new Panel(); // FlowLayout p.add(new Button("OK")); p.add(new Button("Cancel")); add("South",p);

Building Graphical User Interfaces import java.awt.*; Assemble the GUI use GUI components, basic components (e.g., Button, TextField) containers (Frame, Panel) set the positioning of the components use Layout Managers Attach events

A sample GUI program Import java.awt.*; class MyGui { public static void main(String [] s ) { Frame f = new Frame (“My Frame”); Button b = new Button(“OK”); TextField tf = new TextField(“George”, 20); f.setLayout(new FlowLayout()); f.add(b); f.add(tf); f.setSize(300, 300); f.setVisible(true); } }

Events b.addActionListener ( ); method to add a listener listener object Button f.addWindowListener ( ); Frame

Events Each GUI component (e.g., a Button) that wishes to respond to an event type (e.g., click), must register an event handler, called a Listener. The listener is an object of a "Listener" interface. A Listener class can be created by subclassing (through "implements") one of Listener interfaces (all listener inrefaces are in the java.awt.event package = > must import java.awt.event.*; ) The registration of the listener is done by a call to a method such as addActionListener(<Listener Object>). Each GUI component class has one or more such add…() methods, where applicable.

Listener Interfaces INTERFACE NAME (IN JAVA.AWT.EVENT ) [1] ActionListener [2] ItemListener [3] MouseMotionListener [4] MouseListener [5] KeyListener [6] FocusListener [7] AdjustmentListener [8] ComponentListener [9] WindowListener [10] ContainerListener [11] TextListener

Listener Interfaces Each listener interface has methods that need to be implemented for handling different kinds of events. 1) mouseDragged (MouseEvent) - Invoked when a mouse button is pressed on a component and then dragged. 2) mouseMoved (MouseEvent) - Invoked when the mouse button has been moved on a component (with no buttons down). For example, the MouseMotionListener interface has two methods:

1) windowActivated (WindowEvent) - Invoked when a window is activated. 2) windowClosed (WindowEvent) - Invoked when a window has been closed. 3) windowClosing (WindowEvent) - Invoked when a window is in the process of being closed. 4) windowDeactivated (WindowEvent) - Invoked when a window is de-activated. 5) windowDeiconified (WindowEvent) - Invoked when a window is de-iconified. 6) windowIconified (WindowEvent) - Invoked when a window is iconified. 7) windowOpened (WindowEvent) - Invoked when a window has been opened. ... the WindowListener interface has seven methods:

How to create an object of a listener interface ? Interfaces cannot be instantiated. Therefore, cannot do new WindowListener(); Instead, have to subclass the interface and then create object of the subclass

Implementing the ActionListener Interface and attaching an event handler to a button class MyApp implements ActionListener { Button b = new Button(“OK”); public static void main(String [] s ) { ( new MyApp() ).go(); } public void go() { b.addActionListener( this ); } public void actionPerformed(ActionEvent e ) { // what to do when the button is clicked if( e.getSource() == b ) { System.out.println(“OK pressed"); } } }

class MyApp implements ActionListener , WindowListener { Button b = new Button(“OK”); Frame f = new Frame(“My Frame”); public static void main(String [] s ) {( new MyApp() ).go(); } public void go() { b.addActionListener( this ); f.addWindowListener( this ); } public void actionPerformed(ActionEvent e ) { … } public void windowActivated(WindowEvent e ) { … } public void windowClosed(WindowEvent e ) { … } public void windowClosing(WindowEvent e ) { … } public void windowDeactivated(WindowEvent e) { … } public void windowDeiconified(WindowEvent e) { … } public void windowIconified(WindowEvent e) { … } public void windowOpened(WindowEvent e) { … } } Implementing 2 interfaces

or … use Adapters class MyApp extends WindowAdapter { Button b = new Button(“OK”); Frame f = new Frame(“My Frame”); public static void main(String [] s ) {( new MyApp() ).go(); } public void go() { f.addWindowListener( this ); } public void windowClosing(WindowEvent e ) { … } } Need only implement the method(s) that are required, instead of all seven methods of the WindowListener interface

But, we can only use one Adapter at a time (no multiple inheritance) I.e., cannot have : class MyApp extends WindowAdapter, MouseAdapter, ... { … … … ... }

However … can use inner classes instead !!! class MyApp { Button b = new Button(“OK”); Frame f = new Frame(“My Frame”); public static void main(String [] s ) { (( new MyApp() ).go(); } public void go() { f.addWindowListener( new FrameHandler() ); b.addMouseListener( new ButtonHandler() ); } class ButtonHandler extends MouseAdapter { public void mousePressed (MouseEvent e ) { … } } class FrameHandler extends WindowAdapter { public void windowClosing (WindowEvent e ) { … } } }

Popup Menu and Event Handling... //popup.java: popup menu and event handling import java.applet.Applet; import java.awt.*; import java.awt.event.*; public class popup extends Frame implements ActionListener, MouseListener { TextField text1; PopupMenu popup; MenuItem menuitem1, menuitem2, menuitem3; public popup() { super( "Popup Menu" ); setLayout(new FlowLayout()); setBounds(10, 10, 300, 200 ); setVisible(true); init(); } public void init() { popup = new PopupMenu("Resource Usage" );

Popup Menu and Event Handling... menuitem1 = new MenuItem("CPU"); menuitem1.addActionListener(this); menuitem2 = new MenuItem("Disk"); menuitem2.addActionListener(this); menuitem3 = new MenuItem("Memory"); menuitem3.addActionListener(this); popup.add(menuitem1); popup.add(menuitem2); popup.add(menuitem3); add(popup); text1 = new TextField(20); text1.setBounds(20, 40, 120, 30 ); add(text1); addMouseListener(this); } public void mousePressed(MouseEvent e ) { if( e.getModifiers() != 0 ) popup.show(this, e.getX(), e.getY() ); }

Popup Menu and Event Handling public void mouseReleased( MouseEvent e ) { System.out.print("Mouse Released\n" ); } public void mouseEntered( MouseEvent e ) { System.out.print("Mouse Entered\n" ); } public void mouseExited( MouseEvent e ) { System.out.print("Mouse Exited\n" ); } public void actionPerformed( ActionEvent e ) { if( e.getSource() == menuitem1 ) { text1.setText("CPU"); } if( e.getSource() == menuitem2 ) { text1.setText("Disk"); } if( e.getSource() == menuitem3 ) { text1.setText("Memory"); } } public static void main( String args[] ) { popup p = new popup(); } }

AWT & Applets An Applet is a Java program capable of running from within a web page (HTML document) Steps to incorporate and run an applet: · Have MyApplet.java · javac MyApplet.java · Have MyApplet.class · Create MyApplet.html <applet code = MyApplet.class width = 200 height = 300 > </applet> · appletviewer MyApplet.html (or open MyApplet.html in browsers like Netscape/IE).

Applet methods AppletContext “ Applet” derived from AWT Panel Hooks into Browser environment Can be used to link to another Web page Unlike Applications, Applets do not have main(). Instead, they have : init (), start (), stop (), paint (), update (), repaint (), destroy (). All methods need not be implemented -- there are default versions for all of them.

A sample Applet // HelloApplet.java: for processing applet methods import java.awt.*; import java.applet.*; public class HelloApplet extends Applet { public void init() { setBackground(Color.yellow); System.out.println("init() method invoked"); } public void start() { System.out.println("start() method invoked"); } public void paint( Graphics g ) { System.out.println("paint() method invoked"); g.drawString( "Hi there", 24, 25 ); } public void stop() { System.out.println("stop() method invoked"); } }

another sample Applet (run in Applet Viewer)

sample Applet running within Netscape

sample Applet code import java.applet .*; // for Applet class import java.awt .*; // for Graphics class public class MyApplet extends Applet { public void paint ( Graphics g ) { g.drawString("Hi there", 40, 40); g.drawOval(40, 60, 45, 45); g.drawRect(100, 60, 50, 50); g.drawLine(170, 60, 250, 170); } // end paint() public void init () { setBackground(Color.yellow); } } // end class MyApplet

Another example // MyApplet.java: draws rectangle with yellow color fill import java.applet.*; import java.awt.*; public class MyApplet extends Applet { public synchronized void paint(Graphics g) { int x,y,width,height; Dimension dm = size(); x = dm.width/4; y = dm.height / 4; width = dm.width / 2; height = dm.height / 2; // Draw the rectangle in the center with colors! g.setColor(Color.blue); g.drawRect(x,y,width,height); g.setColor(Color.yellow); g.fillRect(x + 1,y + 1,width - 2,height - 2); } }

order of Applet method execution As soon as the browser (or Appletviewer) accesses the page that contains the applet: It calls init(), first It calls start(), second. It calls paint(), third.

order of Applet method execution (cont’d) After the above three initial calls, invocation of the other methods depends on user's activity while in the browser: no activity => none of the methods is invoked leave to a different URL => stop() is invoked (and if later come back to this URL, then start() will be invoked). close down the browser => destroy() is invoked none of the above => either paint() or update() or repaint() is invoked.

Incorporating Images and sound in Applets

sample Applet with sound … … … (MyAppletSound.java)

how to do that …. Step 1 : LOAD (image of sound file) Step 2 : DISPLAY -or- PLAY

Applet that displays image import java.applet.*; import java.awt.*; public class MyApplet1 extends Applet { Image im; public void init () { // load im = getImage(getDocumentBase(),"BOTTOMDOLLAR.JPG"); setBackground(Color.yellow); } public void paint(Graphics g ) { g.drawImage(im, 50, 50, this); // display } } // end class MyApplet1

Applet that plays sound import java.applet.*; import java.awt.*; public class MyAppletSound extends Applet { AudioClip ac; public void init () { // load ac = getAudioClip(getDocumentBase(), "chirp1.au"); } public void start() { ac.loop(); // play } public void stop() { ac.stop(); // stop the sound upon leaving this web page } } // end class MyAppletSound

Multithreading in Java (A built-in feature in Java)

Single and Multithreaded Processes Single-threaded Process Single instruction stream Multiple instruction stream Multiplethreaded Process Threads of Execution Common Address Space threads are light-weight processes within a process

Threads Java has built in thread support for Multithreading Synchronization Thread Scheduling Inter-Thread Communication: currentThread start setPriority yield run getPriority sleep stop suspend resume Java Garbage Collector is a low-priority thread

Thread states new runnable non-runnable dead wait() sleep() suspend() blocked notify() slept resume() unblocked start() stop()

Threading Mechanisms... Create a class that extends the Thread class Create a class that implements the Runnable interface

1st method: Extending Thread class 1st Method: Extending the Thread class class MyThread extends Thread { public void run() { // thread body of execution } } Creating thread: MyThread thr1 = new MyThread(); Start Execution: thr1.start();

An example class MyThread extends Thread { // the thread public void run () { System.out.println(" this thread is running ... "); } } // end class MyThread class ThreadEx2 { // a program that utilizes the thread public static void main(String [] args ) { // note, the created object myThreadObject IS A Thread as well. MyThread t = new MyThread(); // due to extending the Thread class (above) // I can call start(), and this will call // run(). start() is a method in class Thread. t.start(); } // end main() } // end class ThreadEx2

2nd method: Threads by implementing Runnable interface class MyThread implements Runnable { ..... public void run() { // thread body of execution } } Creating Object: MyThread myObject = new MyThread(); Creating Thread Object: Thread thr1 = new Thread( myObject ); Start Execution: thr1.start();

An example class MyThread implements Runnable { public void run() { System.out.println(" this thread is running ... "); } } // end class MyThread class ThreadEx21 { public static void main(String [] args ) { Thread t = new Thread(new MyThread()); // due to implementing the Runnable interface // I can call start(), and this will call run(). t.start(); } // end main() } // end class ThreadEx2

A program with two threads class MyThread implements Runnable { public void run() { System.out.println("This is 'MyThread' ); } } class YourThread implements Runnable { public void run() { System.out.println("This is 'YourThread'); } } class ThreadEx4 { public static void main(String [] args ) { Thread t1 = new Thread(new MyThread()); Thread t2 = new Thread(new YourThread()); t1.start(); t2.start(); } } // end class ThreadEx4

Monitor model (for Syncronisation) Method 1 Method 2 Block 1 Key Threads Monitor (synchronised) solves race-condition problem

examples :: program with two threads and shared object class MyThread implements Runnable { Shared so; public MyThread (Shared s) { so = s;} public void run() { so.method1 (); } } // end class MyThread class YourThread implements Runnable { Shared so; public YourThread (Shared s) { so = s; } public void run() { so.method2 (); } } // end class YourThread class HerThread implements Runnable { Shared so; public HerThread (Shared s) { so = s; } public void run() { so.method3 (); } } // end class HerThread so

the monitor (shared object) class Shared { // the 'monitor' // if 'synchronized' is removed, the outcome is unpredictable public synchronized void method1( ) { for (int i = 0; i < 200; i++) { System.out.print(" [1] :: " + i ) ; } } // if the 'synchronized' is removed, the outcome is unpredictable public synchronized void method2( ) { for (int i = 0; i < 200; i++) { System.out.print(" [2] :: " + i ) ; } } // if the 'synchronized' is removed, the outcome is unpredictable public synchronized void method3( ) { for (int i = 0; i < 200; i++) { System.out.print(" [3] :: " + i ) ; } } } // end class Shared

the driver class MyMainClass { public static void main(String [] args ) { Shared sharedObject = new Shared (); Thread t1 = new Thread(new MyThread( sharedObject )); Thread t2 = new Thread(new YourThread( sharedObject )); Thread t3 = new Thread(new HerThread( sharedObject )); t1.start(); t2.start(); t3.start(); } // end main() } // end class ThreadEx5

Threads in Action... Cooperative threads - File Copy reader() { - - - - - - - - - - lock(buff[i]); read(src,buff[i]); unlock(buff[i]); - - - - - - - - - - } writer() { - - - - - - - - - - lock(buff[i]); write(src,buff[i]); unlock(buff[i]); - - - - - - - - - - } buff[0] buff[1] Cooperative Parallel Synchronized Threads

Streams and I/O basic classes for file IO FileInputStream , for reading from a file FileOutputStream , for writing to a file Example: Open a file "myfile.txt" for reading FileInputStream fis = new FileInputStream("myfile.txt"); Open a file "outfile.txt" for writing FileOutputStream fos = new FileOutputStream ("myfile.txt");

Display File Contents import java.io.*; public class FileToOut1 { public static void main(String args[]) { try { FileInputStream infile = new FileInputStream("testfile.txt"); byte buffer[] = new byte[50]; int nBytesRead; do { nBytesRead = infile.read(buffer); System.out.write(buffer, 0, nBytesRead); } while (nBytesRead == buffer.length); } catch (FileNotFoundException e) { System.err.println("File not found"); } catch (IOException e) { System.err.println("Read failed"); } } }

Filters Once a stream (e.g., file) has been opened, we can attach filters Filters make reading/writing more efficient Most popular filters: For basic types: DataInputStream , DataOutputStream For objects: ObjectInputStream , ObjectOutputStream

Writing data to a file using Filters import java.io.*; public class GenerateData { public static void main(String args[]) { try { FileOutputStream fos = new FileOutputStream("stuff.dat"); DataOutputStream dos = new DataOutputStream(fos); dos.writeInt(2); dos.writeDouble(2.7182818284590451); dos.writeDouble(3.1415926535); dos.close(); fos.close(); } catch (FileNotFoundException e) { System.err.println("File not found"); } catch (IOException e) { System.err.println("Read or write failed"); } } }

Reading data from a file using filters import java.io.*; public class ReadData { public static void main(String args[]) { try { FileInputStream fis = new FileInputStream("stuff.dat"); DataInputStream dis = new DataInputStream(fis); int n = dis.readInt(); System.out.println(n); for( int i = 0; i < n; i++ ) { System.out.println(dis.readDouble()); } dis.close(); fis.close(); } catch (FileNotFoundException e) { System.err.println("File not found"); } catch (IOException e) { System.err.println("Read or write failed"); } } }

Object serialization Write objects to a file, instead of writing primitive types. Use the ObjectInputStream , ObjectOutputStream classes, the same way that filters are used.

Write an object to a file import java.io.*; import java.util.*; public class WriteDate { public WriteDate () { Date d = new Date(); try { FileOutputStream f = new FileOutputStream("date.ser"); ObjectOutputStream s = new ObjectOutputStream (f); s.writeObject (d); s.close (); } catch (IOException e) { e.printStackTrace(); } public static void main (String args[]) { new WriteDate (); } }

Read an object from a file import java.util.*; public class ReadDate { public ReadDate () { Date d = null; ObjectInputStream s = null; try { FileInputStream f = new FileInputStream ("date.ser"); s = new ObjectInputStream (f); } catch (IOException e) { e.printStackTrace(); } try { d = (Date) s.readObject (); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (InvalidClassException e) { e.printStackTrace(); } catch (StreamCorruptedException e) { e.printStackTrace(); } catch (OptionalDataException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } System.out.println ("Date serialized at: "+ d); } public static void main (String args[]) { new ReadDate (); } }

Network/Socket Programming in Java

java.net Used to manage: URL streams Client/server sockets Datagrams

Part III - Networking ServerSocket(1234) Socket(“130.63.122.1”, 1234) Output/write stream Input/read stream Server_name: “cdacb.ernet.in”

Server side Socket Operations 1. Open Server Socket: String server; Socket slink; DataOutputStream os; DataInputStream is; server = new ServerSocket( PORT ); 2. Wait for Client Request: Socket client = server.accept(); 3. Create I/O streams for communicating to clients is = new DataInputStream( client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 4. Perform communication with client Receiive from client: String line = is.readLine(); Send to client: os.writeBytes("Hello\n"); 5. Close sockets: client.close(); For multithreade server: while(true) { i. wait for client requests (step 2 above) ii. create a thread with “client” socket as parameter (the thread creates streams (as in step (3) and does communication as stated in (4). Remove thread once service is provided. }

Client side Socket Operations 1. Get connection to server: client = new Socket( server, port_id ); 2. Create I/O streams for communicating to clients is = new DataInputStream( client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 3. Perform communication with client Receiive from client: String line = is.readLine(); Send to client: os.writeBytes("Hello\n"); 4. Close sockets: client.close();

A simple server (simplified code) import java.net.*; import java.io.*; public class ASimpleServer { public static void main(String args[]) { // Register service on port 1234 ServerSocket s = new ServerSocket(1234); Socket s1=s.accept(); // Wait and accept a connection // Get a communication stream associated with the socket OutputStream s1out = s1.getOutputStream(); DataOutputStream dos = new DataOutputStream (s1out); // Send a string! dos.writeUTF(“Hi there”); // Close the connection, but not the server socket dos.close(); s1out.close(); s1.close(); } }

A simple client (simplified code) import java.net.*; import java.io.*; public class SimpleClient { public static void main(String args[]) throws IOException { // Open your connection to a server, at port 1234 Socket s1 = new Socket(" 130.63.122.1 ",1234); // Get an input file handle from the socket and read the input InputStream s1In = s1.getInputStream(); DataInputStream dis = new DataInputStream(s1In); String st = new String (dis.readUTF()); System.out.println(st); // When done, just close the connection and exit dis.close(); s1In.close(); s1.close(); } }

Echo Server Client.. //client.java: client interface to server import java.io.*; import java.net.*; public class client { int port_id; String server; Socket slink; DataOutputStream os; DataInputStream is; DataInputStream kbd; public client( String args[] ) { server = args[0]; port_id = Integer.valueOf(args[1]).intValue(); try { slink = new Socket( server, port_id ); os = new DataOutputStream( slink.getOutputStream() ); is = new DataInputStream( slink.getInputStream() ); kbd = new DataInputStream( System.in ); }

Echo Server Client.. catch( UnknownHostException e ) { System.err.println( "Don't know about host: " ); System.exit(1); } catch( IOException e ) { System.err.println( "Could not get I/O for the connection to "+server); System.exit(1); } } void communicate() { while(true) { try { System.out.print("Enter Input <end to stop>: "); String line = kbd.readLine(); os.writeBytes( line+"\n" );

Echo Server Client.. if( line.equals("end") ) { os.close(); is.close(); slink.close(); break; } String line2 = is.readLine(); System.out.println("Output: "+line2); } catch( IOException e ) { System.out.println(e); } } } public static void main( String [] args ) { if( args.length < 2 ) { System.out.println("Usage: java client server_name port_id" ); System.exit(1); } client cln = new client( args ); cln.communicate(); } }

Echo Server ... // server.java: echo server import java.io.*; import java.net.*; public class server { // public final static int PORT = 4779; public static void main( String [] args ) { ServerSocket server = null; DataOutputStream os = null; DataInputStream is = null; boolean shutdown = false; if( args.length < 1 ) { System.out.println( "Usage: java server port_num" ); System.exit( 1 ); } int PORT = Integer.valueOf(args[0]).intValue(); try { server = new ServerSocket( PORT ); }

catch( IOException e ) { System.err.println( "Could not get I/O for the connection to: "); } while(!shutdown) { if( server != null ) { try { Socket client = server.accept(); System.out.println("Connected"); InetAddress cip = client.getInetAddress(); System.out.println( "Client IP Addr: "+cip.toString()); is = new DataInputStream( client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); for(;;) { String line = is.readLine(); if( line == null ) break; Echo Server ...

if( line.startsWith("end" ) ) { shutdown = true; break; } os.writeBytes(line.toUpperCase()); os.writeBytes("\n"); System.out.println(line); } is.close(); client.close(); } catch( UnknownHostException e ) { System.err.println( "Server Open fails" ); } catch( IOException e ) { System.err.println( "Could not get I/O for the connection to:"+args[0]); } } } Echo Server ...

System.out.println( "Server Down" ); try { server.close(); } catch(IOException e) {} } } Echo Server

Server Threads Message Passing Facility Server Process Client Process Client Process User Mode Kernel Mode Threads in Action... Multithreaded Server

Java System Architecture & Availability

A Look Inside the Java Platform Java Virtual Machine Porting Interface Applets and Applications Java Base API Java Base Classes Java Standard Extension API Java Standard Extension Classes The Java Base Platform (in black) Network Java on a Browser Java on a Desktop OS Java on a Smaller OS Java on JavaOS Adapter OS Hardware Adapter OS Hardware JavaOS Hardware Adapter Browser OS Hardware

Java Applications! Java applications are now available Cost of manfg zero, cost of distribution zero, cost of marketing zero! Hot Java is lean - loads everything else from the net. Java itself is small - 40k to 225k New class of small machines will emerge Java on cellular phones, credit cards, washing machines, and everywhere ?

Universal Interface Internet Web Servers with JAVA applications Clients running any OS on any platform

Java on my platform ? Sun (SPARC) ftp://java.sun.com Sun(x86) ftp://xm.com:/pub/ IBM(Aix, OS/2)ftp://ncc.hursley.ibm.com/javainfo DEC(Alpha OSF/1) http://www.gr.osf.org:8001/projects/web/java/ SGI http://liawww.epfl.ch/~simon/java/irix-jdk.html HP http://www.gr.osf.org:8001/projects/web/java Linux http://www.blackdown.org AT & T http://www.gr.osf.org:8001/projects/web/java Windows 3.1 http://www.alphaworks.ibm.com

Java Development Tools (Present and Planned)

Sun’s Java WorkShop JDK: Compiler and runtime environment Class Libraries Documentation javadoc - Automated Documentation Takes comments and converts to HTML IDE: Visual Java, and integrated tools, JavaBeans Other Products and API: JavaHelp, Java Card, Java Blend, JavaOS, Java Mail, Java Management, Java Electronic Commerce Framework Java Enterprise API: Java Naming and Directory Interface, Java IDL, JDBC, RMI and Object Serialization

Symantec Cafe 1.0 (Released) Full IDE for Windows 95/NT Graphic Development Tools Two Compilers Debugger Class Browser

Microsoft Jakarta (Planned) Visual C++ type interface Will Support ActiveX/COM Internet Explorer 3.0 will have Just-In-Time Java compiler

Borland JBuilder Visual RAD workbench for maximum productivity. Rapid Application Development (RAD) and Open Component Architecture patterned after Delphi. 100+ JavaBean components, with source code, for drag-and-drop applications. Beans Express --easiest way to create industry-standard Java-Bean components. DataExpress -- the fastest way to build business and database appplications. Borland DataGateway for Java connectivity to all major database servers. Multi-tier applications with integrated RMI and CORBA. Versions : Standard, Professional, & Client/Server

Challenges & Possible Directions Performance AWT - need better GUI! Maintaining Interoperability Security - current restrictions limit what can be done Native Compilers Is Portability that Important?

Comments Java is a fun and easy programming language Portability = Mediocrity? Java will become a programming language of choice, but may take on a final form that will surprise many!

JDBC Java API for Relational Databases Being standardized by all major players

Javascript and Java (Preview) Javascript can control Java applets Static data accessible as properties of applet var i = Bank.Account.count Public methods invocable on Java instances Provided those instances are accessible through the Applet Applet is accessible through document document.applet_Name_Attribute.do_Stuff()

Java for HPC! Many efforts are in in progress for making java as a language for parallel programming. Java computing frameworks (HPC, numeric, data parallel) Java in distributed simulations and applications (e.g., real-world HPC, grand chalenge) Source to source translators (C, Fortran, C++ to Java) Web based computation environment in Java Java for HPC conference: http://www.cs.ucsb.edu/conferences/java98 Java for Science and Engineering computing: subscribe java-for-cse to majordomo@npac.syr.edu http://www.jhpc.org

How to Convert Programs to AWT 1.1... 1. Change source code so that it import event package: import java.awt.event.*; 2. Figure out which component generates each event type: (1.0 uses handleEvent() and action()) Button, List, MenuItem, TextField: Interface: ActionListener Method: actionPerformed(ActionEvent event) Checkbox, CheckboxMenuItem, Choice: Interface: ItemListener Method: itemStateChanged(..) Dialog, Frame: Interface: WindowListener Method: windowClosing(), windowOpened(),...

How to Convert Programs to AWT 1.1... 3. Change class declaration so that class implements public class MyClass extends SomeComponent implements ActionListener 4. Register action Listener newComponentObject.addActionListener(this); 5. Change event handling method: Old: public boolean action(Event e, Object arg) New: public void actionPerformed(ActionEvent e)

How to Convert Programs to AWT 1.1 6. Delete the event handling code in this way (a) Delete all return statements (b) Change e.target to e.getSource() (c) Delete all code the unnecessarily tests for which component the event come from (d) Perform any other modification require to make the program compile

Just to Summarize Java as a Comprehensive Programming Solution Object Oriented Portable High Performance Geared for Distributed Environments Secure Highly suitable for Internet programming

Summary Java is really very well poised Incredible leverage from the Web Will impact the C++ and Smalltalk markets Rate of progress is astonishingly high Development environments CORBA linkages Components Fasten you seat-belts!

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