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Internet and Java Revolutions Impact on Education

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Title: Internet and Java Revolutions Impact on Education


1
Internet and Java Revolutions Impact on Education

Rajkumar School of Computing Queensland
University of Technology Brisbane,
Australia Email rajkumar_at_fit.qut.edu.au URL
http//www.fit.qut.edu.au/rajkumar
2
Motivation
  • Potential delivery sites are widely distributed
  • Information is rapidly changing
  • Connections to the Internet have become
    ubiquitous
  • Different learners have different needs

3
Agenda
  • Internet and its Evolution
  • Internet Tools
  • Web and its Programming
  • Internet as a delivery Vehicle
  • Java for Internet Programming
  • Java Nuts and Bolts
  • Java Platform
  • Developing Applets and Applications
  • Challenges and Future Directions

4
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

5
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

6
Installed base and Growth rate for telephone
lines, mobile phones, and Internet hots
Installed, 1995 1994-95 Growth
Rates () Income Group/ Phone
Mobile Internet Phone Mobile
Internet Region Lines Phones
Hosts Lines Phones Hosts Lower
Income 2.0 0.12 1.35 35.7 135.1 246.0 Lower-
Middle 9.1 0.33 73.31 8.7 105.1 167.0 Upper -
Middle 14.5 1.34 380.13 6.4 66.8 111.9 High 53.
2 8.70 10749.23 3.6 55.6 97.0 Africa 1.7 0.09 69
.14 7.9 60.5 81.4 Americas 29.0 5.17 8359.58 5.
4 42.3 91.5 Asia 5.4 0.62 121.70 14.7 108.3 150.
0 Europe 33.0 3.04 2732.24 3.6 59.5 112.2 Oceans
39.7 9.55 12845.55 4.0 85.7 88.8 World 12.1 1.
56 1661.89 7.0 60.4 97.8
Source ACM, Nov, 97 (phones, international
telecommunication union, hosts, network Wizards
7
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

8
Internet Evolution
Internet everywhere Internet appliances Price
based services Live communities ? ? ? ? ? ? ?
On line connects to internet Secure
payments Multi media Authoring Java VRML HTML
File mail TCP/IP Webpages Netscape
10 of Market
20 of Market
Total Market
9
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

10
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.

11
Viewing WWW pages
  • View text, graphics, pictures, sounds, video
  • Web Browser
  • HyperText Markup Language (HTML)
  • Computer Independent
  • Operating System Independent

12
Web Browsers
  • Netscape Navigator
  • Microsoft Internet Explorer
  • Omni Web
  • NCSA Mosaic
  • Lynx (text only)

13
Internet Organization
  • Truly world-wide
  • Multiple communication media types

14
Internet Organization
Domains .edu .org .com .mil .biz Computers fi
fe.engr.vt.edu www.engr.vt.edu
15
WWW Organization
Client
Client
Server
Server
Server
Client
Server
Client
Client
16
Generating Web Pages
  • Simple Text Editor
  • Word Processor or other tool export
  • e.g., Internet Assistant for Microsoft Word
  • HTML Editor
  • Open file in Netscape Composer
  • Last step is to put the file(s) on an HTML server

17
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.

18
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

19
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

20
How does the Web Work
Send the INFORMATION ABOUT C-DAC ACTS
HTTP
The client sends an HTTP message to a
computer running a Web Server program and asks
for a document
The information about C-DAC ACTS
The web server sends the hypermedia HTML
documents to the client. You end up seeing the
document on your screen
21
HTML document
  • ltHTMLgt
  • ltTITLEgtCentre for Development of Advanced
    Computing
  • lt/TITLEgt
  • ltBODY BGCOLORE7CCCC TEXT000000
    LINK0000FFgt
  • ...
  • ...
  • ltA HREFmailtowebmaster_at_cdacb.ernet.ingt
    webmasterlt/Agt
  • lt/BODYgt
  • lt/HTMLgt

22
(No Transcript)
23
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.ext999/dir1/dir2/dir3/file.h
    tml?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

24
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

25
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

26
Preconfigured v/s Integrated Internet Products
  • Integrated Internet Products- From multiple
    vendors
  • Preconfigured Systems- Web Server and a Client
    ready to use
  • Suns Netra Internet Server
  • SGIs WebFORCE Indy and WebFORCE Challenge S
  • Apples Internet Server Solution
  • DECs Internet AlphaServer
  • Integraphs Web Server 10

27
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

28
Internet in Education
Creating Your Own Page HTML Tags (Title,
Body, images, etc.) Basic HTML code file
structure Links and Anchors Linking it
elsewhere Moving around the WWW Making
it all Look Pretty Use components such as
- WWW Forms, Frames, Sound, Video, -
Animation, WWW Plugins Make web attractive
through Adding web applications -
customer enquiry - Free applications
Institution Web Site - about the
university - faculties and department
details - research facilities, area, and
groups - faculty members details with their
publications Admission Process - course
announcement, - making available details of
course - admission applications, -
announcement of selection University
Facilities - computing facilities,
accommodation, recreation, etc.. Teaching
Process - Use of WWW in the Curriculum -
Homework and Quizzes - Virtual Classroom -
Virtual Lectures - Student Interaction - Q
A
29
Internet as a delivery Vehicle
30
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)

31
Class Sites To Visit
  • http//truth.phil.vt.edu/wwwcourses.html
  • http//http//fiddle.visc.ece.vt.edu/courses/ee250
    4/
  • http//adept.stanford.edu/
  • http//www.aoe.vt.edu/aoe5104.html
  • http//nersp.nerdc.ufl.edu/cgs2422/
  • http//www.sloan.org/oakley/misc/IMNews.html
  • http//www.eng.fsu.edu/net98.html

32
API Bottleneck
MAC
PC
LAN
LAN
Server
Network
SUN
33
The OS - Platform lock
Applications tied to OS OS tied to Platform
Application
Application
OS
Application
34
The Web
Seeded by HTML from CERN Revolutionised by
MOSAIC Standardised, universal interface to
data Graphical
Application
Application
BROWSER
OS
OS
OS
OS
Application
Application
Broadcast capability - publish once, reach
millions
35
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

36
Java and Java Computing
37
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 --

38
Java From 10,000 Ft.
  • According to the world, Java is...
  • According to Sun, Java is...
  • On closer inspection, Java is

39
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

40
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!
41
On Closer Inspection, Java is...
  • Simple
  • Pure
  • Portable
  • Surprisingly effective

42
As a whole, Java is a Comprehensive Programming
Solution
  • Object Oriented
  • Portable
  • High Performance
  • Geared for Distributed Environments
  • Secure

43
Java as Object Oriented
  • Objects all the way down
  • Simple and Familiar C Lite
  • No Pointers!
  • Garbage Collector
  • Dynamic Binding
  • Single Inheritance with Interfaces

44
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

45
Total Platform Independence
JAVA COMPILER
(translator)
JAVA BYTE CODE
(same for all platforms)
JAVA INTERPRETER
(one for each different system)
Windows 95
Macintosh
Solaris
Windows NT
46
Java Write Once, Run Anywhere
47
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

48
Java as High Performance
  • JVM uses lean and mean bytecodes
  • Small binary class filtes
  • Just-in-time Compilers
  • Multithreading
  • Native Methods

49
Java in the World of Distributed Computing
  • Class Loader
  • Lightweight Binary Class Files
  • Multithreading
  • Dynamic
  • Good communication constructs
  • Secure

50
Java as Secure
  • Language designed as safe
  • Strict compiler
  • Dynamic Runtime Loading (Verifier)
  • Runtime Security Manager

51
Object Oriented Languages -a Comparison
52
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

?
53
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

54
  • Java Integrates
  • Power of Compiled Languages
  • and
  • Flexibility of Interpreted Languages

55
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 ltAPPLETgt tag. in html file)

56

Java Environment/ Life Cycle of Java Code
Runtime Environment
Compile-time Environment
Class Loader Bytecode Verifier
Java Class Libraries
Java Source (.java)
Java Bytecodes move locally or through network
Java Virtual machine
Java Compiler
Runtime System
Java Bytecode (.class )
Operating System
Hardware
57
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

58
Hello Internet
  • // hello.java Hello Internet program
  • class HelloInternet
  • public static void main(String args)
  • System.out.println(Hello Internet)

59
Program Processing
  • Compilation
  • javac hello.java
  • results in HelloInternet.class
  • Execution
  • java HelloInternet
  • Hello Internet

60
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)

61
Calling an Applet
  • ltHTMLgt
  • ltTITLEgt Hello Worls Applet lt/TITLEgt
  • ltAPPLET codeHelloWorld.class width500
    height500gt
  • lt/APPLETgt
  • lt/HTMLgt

62
Execution of Applets
4
2
5
3
1
Accessing from CRAY Corp. (USA)
APPLET Development hello.java AT CDAC-India
The browser creates a new window and a new
thread and then runs the code
hello.class AT C-DACS WEB SERVER
Create Applet tag in HTML document
Hello Java
ltapp Hellogt
The Internet
Hello
63
Web Perspective
  • How did Web interactions work?
  • How do they work with Java?
  • Distributed Java objects and the Web

64
Classical Web Perspective
65
Java Web Perspective
66
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/Stoc
    kDemo/standalone.html

67
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

68
Lifecycle of Java Code
69
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

70
Class Loader
  • Unique Namespace for each origin
  • Local namespace classes are called built-ins
  • Prevents class spoofing

71
Security Manager
  • Prevents unauthorized disk read/writes
  • Restricts network access
  • Other access restrictions (native methods)
  • Implementation is browser dependent

72
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

73
Removed From C
  • Operator overloading
  • Pointers and Array/pointers
  • Multiple-inheritance of implementation
  • Enum, typedef, define
  • Copy constructors, destructors
  • Templates
  • And other stuff....

74
Added or Improved over C
  • Interfaces type Vs. class
  • Garbage collection
  • Exceptions (More powerful than C)
  • Strings
  • Instanceof
  • Package
  • Multi-threads

75
Declaring Classes
  • class Queue
  • Object data
  • Queue (int size) // Constructor
  • data new Objectsize
  • void add(Object o)
  • // add to array in class specific
    manner...
  • // other methods

76
Inheritance in Java
  • class PriorityQueue extends Queue
  • PriorityQueue (int size) // Constructor
  • super(size) // Call Queue constructor use
    data
  • // Class specific initialization
  • void add(Object o) // Overriden method
  • // add to array in class specific
    manner...
  • // other methods

77
Creating and Using Objects
  • PriorityQueue p new PriorityQueue(10) // Q of
    size 10
  • String s This is a string
  • p.add(s) // Add string to priority queue
  • p.add(this) // Add object calling this code to
    queue...

78
Class Methods and Variables
  • int pi Math.PI
  • int theMax Math.max(x,6)
  • Definitions
  • public final static double PI
  • 3.14159265358979323846
  • public static int max(int a, int b)

79
Access Rules
  • public
  • private
  • protected
  • package (Default - no keyword)

80
Using Threads
  • Define a Thread class
  • public MyThread extends Thread
  • public void run() // Override default
    method
  • while (true) // do custom code
  • .
  • Using the thread
  • MyThread t new MyThread()
  • t.start() // Start the thread...
  • Detailed discussion on Threads, later

81
Strings
  • The language defines strings as objects
  • doSomething("abc" "cde")
  • doSomething(String s) ..
  • String abc new String(Hello)
  • System.out.println(abc)

82
Exceptions
  • Try, catch, throw, finally
  • try failure_Prone_Call()
  • catch (File_Exception f) ....Handle f....
  • finally do_This_Regardless()
  • Exception signatures are checked void foo()
    throws TypeC
  • Exceptions must be caught or declared
  • Errors do not have to be caught
  • Surprisingly effective at producing robust code

83
Exception Handling
  • try
  • // some code here...
  • int x y/z
  • catch (ArithmeticException e)
  • System.out.println(Divide by zero error!)
  • catch (Exception e)
  • System.out.println(Some other error!)
  • finally // Optional...
  • z

84
More about Exceptions
  • Very Strict Exception Handling Rules
  • All methods that throw an exception must be
    caught or rethrown (except for runtime
    exceptions)
  • Hierarchy of Exception classes
  • Can create custom Exception classes
  • Cause own exception with throw clause

85
Interfaces
  • Interfaces are a way to declare an Abstract type
    without implementation
  • Interfaces are like classes but without
    implementation
  • Interfaces are expressions of pure designs only
  • Example Interface
  • interface sqrt
  • int sqrt(int newint)
  • Implementing an interface
  • class myclass implements sqrt
  • ..........

86
Interface Type and Sub-Type
  • Pure type of a set of objects
  • interface Observer
  • void update (Observable o)
  • Interfaces can form a graph
  • interface List_Observer extends Observer
  • void updateItem (int position)

87
Class Implements Interface
  • Complete type/class separation possible
  • class Order implements Observer
  • public void update (Object o)
  • // do stuff toupdate
  • // data and other implementation
  • Any object can support multiple interfaces
  • Client can see its types separately or conjoined
  • A powerful approach to design, roles,
    distribution, design patterns
  • Takes a little bit of getting used to

88
Implementation Inheritance
  • Single inheritance of implementation
  • class X extends W implements E, F
  • // Stuff in class X

89
Interfaces and Classes!
90
Uses of Interfaces
  • There are considerable problems due to Multiple
    Inheritance
  • Interfaces in a way add multiple inheritance to
    Java
  • Interfaces may be extended too, more than once

91
Garbage Collected
  • No more manual memory management
  • class Recycler
  • public void recycle ()
  • Hashtable t
  • for (int i0 ilt100 i)
  • t new Hashtable()
  • Significant elimination of programming bugs

92
instanceof and casts
  • Run-time type query
  • void foo (Object x)
  • if (x instanceof Order)
  • Order o (Order) x
  • // ...Do stuff with o
  • Can query for an interface or a class

93
Packages
  • No more include
  • package Shopper
  • import java.awt.
  • // define Shopper interfaces and classes
  • Provides namespace and export features
  • class, sub-class, intra-package, and inter
    package control
  • Package typically maps to a directory

94
Packages and Utilities
  • Packages - helps in organizeing classes i.e.,
    keep the class name space compartmentalized
  • For Naming and Visibility
  • Similar to C Class Libraries
  • Bring in classes from other packages with the
    import keyowrd
  • Ad hoc collection of utility classes
  • Storing collection of objects
  • Interfacing with low-level system functions
  • Math functions (java.lang.Math)

95
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

96
Main Packages
  • java.lang
  • java.util
  • java.io
  • java.awt
  • java.awt.image
  • java.applet
  • java.net

97
java.lang Core Classes
  • Base Class Object
  • String
  • String s This is number 6
  • Math
  • Math.sqrt(4.0)
  • System
  • System.out.println(An error occurred)
  • System.exit(1)

98
java.lang Type Wrappers
  • Literals int, double, boolean, char
  • Literals wrapped in Classes Integer, Double,
    Boolean, Character
  • Literals used for high performance
  • Examples
  • int x Integer.parseInt(6)
  • Integer I new Integer(999)
  • double dbl I.doubleValue()//Returns 999.000

99
java.io - Filtering input streams
  • try // Open the file...
  • DataInputStream dis new DataInputStream(
    new BufferedInputStream(
  • new FileInputStream(myFile)) )
  • // Read lines until EOF is reached...
  • String s
  • while((s dis.readLine()) ! null) //
    Read CR delimited lines
  • System.out.println(s)
  • dis.close()
  • // Handle any exceptions caused by the
    process...
  • catch (IOException e)
  • System.out.println(e.getMessage())

100
GUI Programming in Java (AWT and Event Handling)
101
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

102
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

103
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)

104
Adding Components via Layouts
105
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()

106
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() )

107
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()

108
Custom Drawing
  • // 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)

109
java.applet
  • Applet
  • Class representation of applet
  • init() method called when first loaded
  • start() when applets Web page becomes active
  • stop() when user leaves Web Page
  • Actually derived from AWT Panel
  • AppletContext
  • Hooks into Browser environment
  • Can be used to link to another Web page

110
A sample Applet
  • // HelloApplet.java for processing applet
    methods
  • import java.awt.
  • import java.applet.
  • public class HelloApplet extends Applet
  • public void init()
  • 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( "Hello World", 24, 25 )
  • public void stop()

111
Network/Socket Programming in Java
112
java.net
  • Used to manage
  • URL streams
  • Client/server sockets
  • Datagrams

113
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.getOutputStre
    am() )
  • 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.

114
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.getOutputStre
    am() )
  • 3. Perform communication with client
  • Receiive from client String line
    is.readLine()
  • Send to client os.writeBytes("Hello\n")
  • 4. Close sockets client.close()

115
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 args0
  • port_id Integer.valueOf(args1).intValue(
    )
  • try
  • slink new Socket( server, port_id )
  • os new DataOutputStream(
    slink.getOutputStream() )
  • is new DataInputStream(
    slink.getInputStream() )

116
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 ltend to
    stopgt ")
  • String line kbd.readLine()
  • os.writeBytes( line"\n" )

117
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 lt 2 )
  • System.out.println("Usage java client
    server_name port_id" )
  • System.exit(1)
  • client cln new client( args )

118
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 lt 1 )
  • System.out.println( "Usage java server
    port_num" )
  • System.exit( 1 )
  • int PORT Integer.valueOf(args0).intValue
    ()
  • try

119
Echo Server ...
  • 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.getInetAddres
    s()
  • System.out.println( "Client IP Addr
    "cip.toString())
  • is new DataInputStream(
    client.getInputStream() )
  • os new DataOutputStream(
    client.getOutputStream() )
  • for()
  • String line is.readLine()

120
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"args0)

121
Echo Server
  • System.out.println( "Server Down" )
  • try
  • server.close()
  • catch(IOException e)

122
Multithreading in Java (A built-in feature in
Java)
123
What are Threads?
  • Thread is a piece of code that can execute in
    concurrence with other threads.
  • It is a schedule entity on a processor
  • Local state
  • Global/ shared state
  • PC
  • Hard/Software Context

Thread Object
124
Single and Multithreaded Processes
Single-threaded Process
Multiplethreaded Process
Threads of Execution
Multiple instruction stream
Single instruction stream
Common Address Space
125
OS Multi-Processing, Multi-Threaded
Threaded Libraries, Multi-threaded I/O
Better Response Times in Multiple Application
Environments
Higher Throughput for Parallelizeable Applications
126
Threaded Process Model
THREAD STACK
SHARED MEMORY
THREAD DATA
Threads within a process
THREAD TEXT
  • Independent executables
  • All threads are parts of a process hence
    communication
  • easier and simpler.

127
Levels of Parallelism Thread Granularity
Code-Granularity Code Item Large grain (task
level) Program Medium grain (control
level) Function (thread) Fine grain (data
level) Loop Very fine grain (multiple
issue) With hardware
Task i-l
Task i
Task i1
func1 ( ) .... ....
func2 ( ) .... ....
func3 ( ) .... ....
  • Task
  • Control
  • Data
  • Multiple Issue

a ( 0 ) .. b ( 0 ) ..
a ( 1 ).. b ( 1 )..
a ( 2 ).. b ( 2 )..

x
Load
128
Multithreading - Uniprocessors
  • Concurrency Vs Parallelism
  • Concurrency

P1
CPU
P2
P3
time
Number of Simulatneous execution units gt no of
CPUs
129
Multithreading - Multiprocessors
Concurrency Vs Parallelism
CPU
P1
CPU
P2
CPU
P3
time
No of execution process no of CPUs
130
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

131
Threading Mechanisms...
  • Create a class that extends the Thread class
  • Create a class that implements the Runnable
    interface

132
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()

133
2nd method Threads by implementing Runnable
interface
  • class ClassName implements Runnable
  • .....
  • public void run()
  • // thread body of execution
  • Creating Object
  • ClassName myObject new ClassName()
  • Creating Thread Object
  • Thread thr1 new Thread( myObject )
  • Start Execution
  • thr1.start()

134
Multi-Threaded
  • Thread and its subclasses run one thread per
    instance
  • class MyThread extends Thread public void run
    () ...Start running
  • Any Runnable object can wrap a thread around
    itself
  • class Server implements Runnable Thread t
    Server () t new Thread(this) .
  • public void run () ...Start running
  • Thread control Thread.start(), Thread.stop()

135
Manipulation of Current Thread
  • // CurrentThreadDemo.java
  • class CurrentThreadDemo
  • public static void main(String arg)
  • Thread ct Thread.currentThread()
  • ct.setName( "My Thread" )
  • System.out.println("Current Thread "ct)
  • try
  • for(int i5 igt0 i--)
  • System.out.println(" " i)
  • Thread.sleep(1000)
  • catch(InterruptedException e)
  • System.out.println("Interrupted.")
  • Run
  • Current Thread ThreadMy Thread,5,main
  • 5

136
Creating new Thread...
  • // ThreadDemo.java
  • class ThreadDemo implements Runnable
  • ThreadDemo()
  • Thread ct Thread.currentThread()
  • System.out.println("Current Thread "ct)
  • Thread t new Thread(this,"Demo Thread")
  • t.start()
  • try
  • Thread.sleep(3000)
  • catch(InterruptedException e)
  • System.out.println("Interrupted.")
  • System.out.println("Exiting main thread.")

137
...Creating new Thread.
  • public void run()
  • try
  • for(int i5 igt0 i--)
  • System.out.println(" " i)
  • Thread.sleep(1000)
  • catch(InterruptedException e)
  • System.out.println("Child interrupted.")
  • System.out.println("Exiting child
    thread.")
  • public static void main(String args)
  • new ThreadDemo()
  • Run
  • Current Thread Threadmain,5,main
  • 5
  • 4
  • 3

138
Thread Priority...
  • // HiLoPri.java
  • class Clicker implements Runnable
  • int click 0
  • private Thread t
  • private boolean running true
  • public Clicker(int p)
  • t new Thread(this)
  • t.setPriority(p)
  • public void run()
  • while(running)
  • click
  • public void start()
  • t.start()
  • public void stop()
  • running false

139
...Thread Priority
  • class HiLoPri
  • public static void main(String args)
  • Thread.currentThread().setPriority(Thread.MA
    X_PRIORITY)
  • Clicker Hi new Clicker(Thread.NORM_PRIORIT
    Y2)
  • Clicker Lo new Clicker(Thread.NORM_PRIORIT
    Y-2)
  • Lo.start()
  • Hi.start()
  • try Thread.sleep(10000)
  • catch (Exception e)
  • Lo.stop()
  • Hi.stop()
  • System.out.println(Lo.click " vs. "
    Hi.click)
  • Run1 (on Solaris)
  • 0 vs. 956228
  • Run2 (Window 95)

140
Threads Need Synchronization
  • Server instances lock themselves at method-level
  • class Buffer // synchronize on buffer instance
    public synchronized void put (int i) ...
  • public synchronized int get () . void safe () .
  • Client instance locks a server object before
    using it
  • synchronized (array_to_sort) ..... wait() //
    within synchronized methodnotify()
  • notifyall() // wake up from a wait

141
Monitor model (for Syncronisation)
Method 1
Method 2
Key
Block 1
Threads
Monitor (synchronised) solves race-condition
problem
142
Threads Synchronisation...
  • // Synch.java race-condition without
    synchronisation
  • class Callme
  • // Check synchronized and unsynchronized
    methods
  • / synchronized / void call(String msg)
  • System.out.print(""msg)
  • try Thread.sleep(1000)
  • catch(Exception e)
  • System.out.println("")
  • class Caller implements Runnable
  • String msg
  • Callme Target
  • public Caller(Callme t, String s)
  • Target t
  • msg s

143
...Threads Synchronisation.
  • public void run()
  • Target.call(msg)
  • class Synch
  • public static void main(String args)
  • Callme Target new Callme()
  • new Caller(Target, "Hello")
  • new Caller(Target, "Synchronized")
  • new Caller(Target, "World")
  • Run 1 With unsynchronized call method (race
    condition)
  • HelloSynchronizedWorld
  • Run 2 With synchronized call method
  • Hello
  • Synchronized

144
Queue (no inter-threaded communication)...
  • // pc.java produce and consumer
  • class Queue
  • int n
  • synchronized int get()
  • System.out.println("Got "n)
  • return n
  • synchronized void put(int n)
  • this.n n
  • System.out.println("Put "n)
  • class Producer implements Runnable
  • Queue Q
  • Producer(Queue q)
  • Q q

145
Queue (no inter-threaded communication)...
  • public void run()
  • int i 0
  • while(true)
  • Q.put(i)
  • class Consumer implements Runnable
  • Queue Q
  • Consumer(Queue q)
  • Q q
  • new Thread( this, "Consumer").start()
  • public void run()
  • while(true)
  • Q.get()

146
...Queue (no inter-threaded communication).
  • class PC
  • public static void main(String args)
  • Queue Q new Queue()
  • new Producer(Q)
  • new Consumer(Q)
  • Run
  • Put 1
  • Got 1
  • Got 1
  • Got 1
  • Put 2
  • Put 3
  • Got 3
  • C

147
Queue (interthread communication)...
  • // PCnew.java produce-consumenr with interthread
    communication
  • class Queue
  • int n
  • boolean ValueSet false
  • synchronized int get()
  • try
  • if(!ValueSet)
  • wait()
  • catch(InterruptedException e)
  • System.out.println("Got "n)
  • ValueSet false
  • notify()
  • return n

148
Queue (interthread communication)...
  • synchronized void put(int n)
  • try
  • if(ValueSet)
  • wait()
  • catch(InterruptedException e)
  • this.n n
  • System.out.println("Put "n)
  • ValueSet true
  • notify()
  • class Producer implements Runnable
  • Queue Q
  • Producer(Queue q)
  • Q q

149
Queue (interthread communication)...
  • public void run()
  • int i 0
  • while(true)
  • Q.put(i)
  • class Consumer implements Runnable
  • Queue Q
  • Consumer(Queue q)
  • Q q
  • new Thread( this, "Consumer").start()
  • public void run()
  • while(true)
  • Q.get()

150
...Queue (no interthread communication).
  • class PCnew
  • public static void main(String args)
  • Queue Q new Queue()
  • new Producer(Q)
  • new Consumer(Q)
  • Run
  • Put 0
  • Got 0
  • Put 1
  • Got 1
  • Put 2
  • Got 2
  • Put 3
  • Got 3
  • Put 4

151
Deadlock...
  • // DeadLock.java
  • class A
  • synchronized void foo(B b)
  • String name Thread.currentThread().getName
    ()
  • System.out.println(name " entered
    A.foo")
  • try
  • Thread.sleep(1000)
  • catch(Exception e)
  • System.out.println(name " trying to call
    B.last()")
  • b.last()
  • synchronized void last()

152
Deadlock...
  • class B
  • synchronized void bar(A a)
  • String name Thread.currentThread().getName
    ()
  • System.out.println(name " entered
    B.bar")
  • try
  • Thread.sleep(1000)
  • catch(Exception e)
  • System.out.println(name " trying to call
    A.last()")
  • a.last()
  • synchronized void last()

153
...Deadlock.
  • class DeadLock implements Runnable
  • A a new A() B b new B()
  • DeadLock()
  • Thread.currentThread().setName("Main
    Thread")
  • new Thread(this).start()
  • a.foo(b)
  • System.out.println("Back in the main
    thread.")
  • public void run()
  • Thread.currentThread().setName("Racing
    Thread")
  • b.bar(a) System.out.println("Back in the
    other thread")
  • public static void main(String args)
  • new DeadLock()
  • Run
  • Main Thread entered A.foo
  • Racing Thread entered B.bar

154
Threads in Action... Cooperative threads - File
Copy
reader() - - - - - - - - - - lock(buffi) read
(src,buffi) unlock(buffi) - - - - - - - - -
-
writer() - - - - - - - - - - lock(buffi) writ
e(src,buffi) unlock(buffi) - - - - - - - -
- -
buff0
buff1
Cooperative Parallel Synchronized Threads
155
Threads in Action... Multithreaded Server
Server Process
Client Process
Server Threads
Client Process
User Mode
Kernel Mode
Message Passing Facility
156
A Look Inside the Java Platform
Applets and Applications
Java Base API Java Base Classes
Java Standard Extension API Java Standard
Extension Classes
The Java Base Platform (in black)
Java Virtual Machine
Porting Interface
Network
Java on a Browser
Java on a Desktop OS
Java on a Smaller OS
Java on JavaOS
157
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 ?

158
Universal Interface
Web Servers with JAVA applications
Internet
Clients running any OS on any platform
159
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.org8001/projec
    ts/web/java/
  • SGI http//liawww.epfl.ch/simon/java/irix-jdk.htm
    l
  • HP http//www.gr.osf.org8001/projects/web/java
  • Linux http//www.blackdown.org
  • AT T http//www.gr.osf.org8001/projects/web/jav
    a
  • Windows 3.1 http//www.alphaworks.ibm.com

160
Java Development Tools (Present and Planned)
161
Suns 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

162
Symantec Cafe 1.0 (Released)
  • Full IDE for Windows 95/NT
  • Graphic Development Tools
  • Two Compilers
  • Debugger
  • Class Browser

163
Microsoft Jakarta (Planned)
  • Visual C type interface
  • Will Support ActiveX/COM
  • Internet Explorer 3.0 will have Just-In-Time Java
    compiler

164
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

165
Challenges Possible Directions
  • Performance
  • AWT - need better GUI!
  • Maintaining Interoperability
  • Security - current restrictions limit what can be
    done
  • Native Compilers
  • Is Portability that Important?

166
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!

167
JDBC
  • Java API for Relational Databases
  • Being standardized by all major players

168
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_S
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