A programmer s introduction to java
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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

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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


Purpose

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

  • 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


A programmer s introduction to java

Mechanics

Comments

/**

* 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


Compilation

Compilation

Javac - the compiler from Sun

HellloWorld.java

Source Code

suffix

HellloWorld.class

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


A programmer s introduction to java

JSDK

  • 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


Recap

Recap

  • 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


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