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A Programmer's Introduction to Java. - from a S/370 user. (c) IDMS/SQL News http://www.geocities.com/idmssql. Purpose. There seems to be a wall between the ‘old’ mainframe guys and the new Javaworld The wall is artificially created using buzzwords as the building blocks

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a programmer s introduction to java

A Programmer's Introduction to Java

- from a S/370 user

(c) IDMS/SQL News http://www.geocities.com/idmssql

  • There seems to be a wall between the ‘old’ mainframe guys and the new Javaworld
  • The wall is artificially created using buzzwords as the building blocks
  • Our objective is to remove this wall
  • Course will focus on where Java approach differs from our traditional programming

Java - Introduction (c)http://www.geocities.com/idmssql

java topics
Java - Topics
  • Buzzwords and the Reality
  • Basic Data Structures in Java
  • JSDK from Sun
  • Arrays
  • OOP Basics, Classes and Methods
  • Constructor
  • File Handling -I/O- Data Streams
  • GUI - AWT and Swing Components
  • Method Overloading, Polymorphism
  • Applets
  • IDEs - Intgrated Development Environments

Java - Introduction (c)http://www.geocities.com/idmssql

what is java
What is Java?
  • “Java: A simple, object-oriented, network-savvy, interpreted, robust, secure, architecture-neutral, portable, high-performance, multithreaded, dynamic language”

--Sun Microsystems

  • The words have been faithfully copied from the original article by James Gosling (1995)
  • Simple meant simpler than C++! Gosling never intended to compare with other platforms or languages!

Java - Introduction (c)http://www.geocities.com/idmssql

a more realistic definition
A more realistic definition:
  • A C++ like OO language that has a readable syntax and acceptable performance designed to run on several modern platforms.
  • eg: applications servers, web servers, web browser (embedded in), Mobile phones and ordinary Windows applications

Java - Introduction (c)http://www.geocities.com/idmssql

evolution of java
Evolution of Java
  • James Gosling, Arthur Van hoff, Andy Bechtolsheim. The Original Team in Sun
  • Originally designed to work in appliances
  • Mutated to a web browser environment (client)
  • Mutated from there to server software, where it can run on many back-end server platforms without worrying about GUI compatibility problems

Java - Introduction (c)http://www.geocities.com/idmssql

java syntax
Java Syntax
  • Language syntax itself is simple
  • Data type declarations, mathematical operations, array definitions , if-else, for loop, do-while etc are not complex
  • Easier than C++
  • Though a few idiosyncracies inherited from C++

Java - Introduction (c)http://www.geocities.com/idmssql

sample program
Sample Program

/** Hello World in Java */

public class HelloWorld {

public static void main (String args[]) {

System.out.println("Hello S212 World!");

} // end of method main

} // end of class

Java - Introduction (c)http://www.geocities.com/idmssql





* HelloWorld.java


public class HelloWorld extends Object


public static void main(String arguments[]) // Where the program starts


System.out.println(“Hello World"); // Print out message



Class name (MUST match file name)

Main method (starting point)

Line comment

Braces ‘{}’ - start & end of class and methods

Java - Introduction (c)http://www.geocities.com/idmssql

classes and methods
Classes and Methods

We see that Java programs are organized as

classes and methods

All Java programs start with a class definition

Classes contain one or more methods

Java - Introduction (c)http://www.geocities.com/idmssql


Javac - the compiler from Sun


Source Code



Byte Code

Java Virtual Machine

Run time

Source code is translated to an intermediate “byte code”

The byte code is run in a Java Run Time System which is normally known as JVM = Java Virtual Machine

Java - Introduction (c)http://www.geocities.com/idmssql

jsdk development kit
JSDK – Development Kit
  • Standard Edition is free - from Sun
  • Contains compilers like
  • - Javac - compile
  • - Java - execute
  • - appletviewer – run applets
  • - Javap – dis-assembler
  • - Javadoc - created html based doc
  • - Jar – Java Archive Tool (ZIP)
  • - many smaller tools...

Java - Introduction (c)http://www.geocities.com/idmssql

  • Good
  • Unlike C, others vendors didn’t bother to make their own compilers – one is enough!
  • Easy to install and run
  • Documentation available from sun (zip format)
  • Missing : Sun failed to give a simple editor and test environment; One must go to DOS! And use an editor made by Mr Nobody!!!

Java - Introduction (c)http://www.geocities.com/idmssql

java vs c
Java vs C
  • Java was designed for a specific purpose
  • C is a more general purpose closer-to-machine language
  • Java does not produce machine code; “interpreted” by the Java Run Time (JVM)
  • C produces executable code (*.exe) which can be run as it is

Java - Introduction (c)http://www.geocities.com/idmssql

  • Java is an Object Oriented language suitable for Web and Server based Windows applications
  • Java SDK from Sun gives you the compiler and Runtime for Java
  • It’s all about classes and methods

Java - Introduction (c)http://www.geocities.com/idmssql