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Java Tutorial


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Java is a high-level programming language originally developed by Sun Microsystems and released in 1995.

Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. This tutorial gives a complete understanding on Java.

Java programming language was originally developed by Sun Microsystems, which was initiated by James Gosling and released in 1995 as core component of Sun Microsystems.s Java platform (Java 1.0 [J2SE]).

As of December 08 the latest release of the Java Standard Edition is 6 (J2SE). With the advancement of Java and its wide spread popularity, multiple configurations were built to suite various types of platforms. Ex: J2EE for Enterprise Applications, J2ME for Mobile Applications.

Sun Microsystems has renamed the new J2 versions as Java SE, Java EE and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere

Java is:

    Object Oriented : In java everything is an Object. Java can be easily extended since it is based on the Object model.

    Platform independent: Unlike many other programming languages including C and C++ when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by virtual Machine (JVM) on whichever platform it is being run.

    Simple :Java is designed to be easy to learn. If you understand the basic concept of OOP java would be easy to master.

    Secure : With Java.s secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are based on public-key encryption.

    Architectural- neutral :Java compiler generates an architecture-neutral object file format which makes the compiled code to be executable on many processors, with the presence Java runtime system.

    Portable :being architectural neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler and Java is written in ANSI C with a clean portability boundary which is a POSIX subset.

    Robust :Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking.

    Multi-threaded : With Java.s multi-threaded feature it is possible to write programs that can do many tasks simultaneously. This design feature allows developers to construct smoothly running interactive applications.

    Interpreted :Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light weight process.

    High Performance: With the use of Just-In-Time compilers Java enables high performance.

    Distributed :Java is designed for the distributed environment of the internet.

    Dynamic : Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.

History of Java:

James Gosling initiated the Java language project in June 1991 for use in one of his many set-top box projects. The language, initially called Oak after an oak tree that stood outside Gosling's office, also went by the name Green and ended up later renamed as Java, from a list of random words.

Sun released the first public implementation as Java 1.0 in 1995. It promised Write Once, Run Anywhere (WORA), providing no-cost run-times on popular platforms.

On 13 November 2006, Sun released much of Java as free and open source software under the terms of the GNU General Public License (GPL).

On 8 May 2007 Sun finished the process, making all of Java's core code free and open-source, aside from a small portion of code to which Sun did not hold the copyright.
Tools you will need:

For performing the examples discussed in this tutorial, you will need a Pentium 200-MHz computer with a minimum of 64 MB of RAM (128 MB of RAM recommended).

You also will need the following softwares:

    Linux 7.1 or Windows 95/98/2000/XP operating system.

    Java JDK 5

    Microsoft Notepad or any other text editor

This tutorial will provide the necessary skills to create GUI, networking, and Web applications using Java.
What is Next ?

Next chapter will guide you to where you can obtain Java and its documentation. Finally, it instructs you on how to install Java and prepare an environment to develop Java applications.

Before we proceed further it is important that we set up the java environment correctly. This section guides you on how to download and set up Java on your machine. Please follow the following steps to set up the environment.

Java SE is freely available from the link Download Java. So you download a version based on your operating system.

Follow the instructions to download java and run the .exe to install Java on your machine. Once you installed Java on your machine, you would need to set environment variables to point to correct installation directories:
Setting up the path for windows 2000/XP:

Assuming you have installed Java in c:\Program Files\java\jdk directory:

    Right-click on 'My Computer' and select 'Properties'.

    Click on the 'Environment variables' button under the 'Advanced' tab.

    Now alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.

Setting up the path for windows 95/98/ME:

Assuming you have installed Java in c:\Program Files\java\jdk directory:

    Edit the 'C:\autoexec.bat' file and add the following line at the end:
    'SET PATH=%PATH%;C:\Program Files\java\jdk\bin'

Setting up the path for Linux, UNIX, Solaris, FreeBSD:

Environment variable PATH should be set to point to where the java binaries have been installed. Refer to your shell documentation if you have trouble doing this.

Example, if you use bash as your shell, then you would add the following line to the end of your '.bashrc: export PATH=/path/to/java:$PATH'
Popular Java Editors:

To write your java programs you will need a text editor. There are even more sophisticated IDE available in the market. But for now, you can consider one of the following:

    Notepad : On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.

    Netbeans :is a Java IDE that is open source and free which can be downloaded from http://www.netbeans.org/index.html.

    Eclipse : is also a java IDE developed by the eclipse open source community and can be downloaded from http://www.eclipse.org/.

What is Next ?

Next chapter will teach you how to write and run your first java program and some of the important basic syntaxes in java needed for developing applications.

When we consider a Java program it can be defined as a collection of objects that communicate via invoking each others methods. Let us now briefly look into what do class, object, methods and instant variables mean.

    Object - Objects have states and behaviors. Example: A dog has states-color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.

    Class - A class can be defined as a template/ blue print that describe the behaviors/states that object of its type support.

    Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.

    Instant Variables - Each object has its unique set of instant variables. An object.s state is created by the values assigned to these instant variables.

First Java Program:

Let us look at a simple code that would print the words Hello World.

public class MyFirstJavaProgram{

  /* This is my first java program. 
    * This will print 'Hello World' as the output

    public static void main(String []args){
      System.out.println("Hello World"); // prints Hello World

Lets look at how to save the file, compile and run the program. Please follow the steps given below:

    Open notepad and add the code as above.

    Save the file as : MyFirstJavaProgram.java.

    Open a command prompt window and go o the directory where you saved the class. Assume its C:\.

    Type ' javac MyFirstJavaProgram.java ' and press enter to compile your code. If there are no errors in your code the command prompt will take you to the next line.( Assumption : The path variable is set).

    Now type ' java MyFirstJavaProgram ' to run your program.

    You will be able to see ' Hello World ' printed on the window.

C : > javac MyFirstJavaProgram.java
C : > java MyFirstJavaProgram
Hello World

Basic Syntax:

About Java programs, it is very important to keep in mind the following points.

    Case Sensitivity - Java is case sensitive which means identifier Hello and hello would have different meaning in Java.

    Class Names - For all class names the first letter should be in Upper Case.

    If several words are used to form a name of the class each inner words first letter should be in Upper Case.

    Example class MyFirstJavaClass

    Method Names - All method names should start with a Lower Case letter.

    If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.

    Example public void myMethodName()

    Program File Name - Name of the program file should exactly match the class name.

    When saving the file you should save it using the class name (Remember java is case sensitive) and append '.java' to the end of the name. (if the file name and the class name do not match your program will not compile).

    Example : Assume 'MyFirstJavaProgram' is the class name. Then the file should be saved as 'MyFirstJavaProgram.java'

    public static void main(String args[]) - java program processing starts from the main() method which is a mandatory part of every java program..

Java Identifiers:

All java components require names. Names used for classes, variables and methods are called identifiers.

In java there are several points to remember about identifiers. They are as follows:

    All identifiers should begin with a letter (A to Z or a to z ), currency character ($) or an underscore (-).

    After the first character identifiers can have any combination of characters.

    A key word cannot be used as an identifier.

    Most importantly identifiers are case sensitive.

    Examples of legal identifiers:age, $salary, _value, __1_value

    Examples of illegal identifiers : 123abc, -salary

Java Modifiers:

Like other languages it is possible to modify classes, methods etc by using modifiers. There are two categories of modifiers.

    Access Modifiers : defualt, public , protected, private

    Non-access Modifiers : final, abstract, strictfp

We will be looking into more details about modifiers in the next section.
Java Variables:

We would see following type of variables in Java:

    Local Variables
    Class Variables (Static Variables)
    Instance Variables (Non static variables)

Java Arrays:

Arrays are objects that store multiple variables of the same type. However an Array itself is an object on the heap. We will look into how to declare, construct and initialize in the upcoming chapters.
Java Enums:

Enums were introduced in java 5.0. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums.

With the use of enums it is possible to reduce the number of bugs in your code.

For example if we consider an application for a fresh juice shop it would be possible to restrict the glass size to small, medium and Large. This would make sure that it would not allow anyone to order any size other than the small, medium or large.

class  FreshJuice{
  enum FreshJuiceSize{ SMALL, MEDUIM, LARGE }
  FreshJuiceSize size;

public class FreshJuiceTest{
  public static void main(String args[]){
      FreshJuice juice = new FreshJuice();
      juice.size = FreshJuice. FreshJuiceSize.MEDUIM ;

Note: enums can be declared as their own or inside a class. Methods, variables, constructors can be defined inside enums as well.
Java Keywords:

The following list shows the reserved words in Java. These reserved words may not be used as constant or variable or any other identifier names.
abstract assert boolean break
byte case catch char
class const continue default
do double else enum
extends final finally float
for goto if implements
import instanceof int interface
long native new package
private protected public return
short static strictfp super
switch synchronized this throw
throws transient try void
volatile while
Comments in Java

Java supports single line and multi-line comments very similar to c and c++. All characters available inside any comment are ignored by Java compiler.

public class MyFirstJavaProgram{

  /* This is my first java program.
    * This will print 'Hello World' as the output
    * This is an example of multi-line comments.

    public static void main(String []args){
      // This is an example of single line comment
      /* This is also an example of single line comment. */
      System.out.println("Hello World");

Using Blank Lines:

A line containing only whitespace, possibly with a comment, is known as a blank line, and Java totally ignores it.

In java classes can be derived from classes. Basically if you need to create a new class and here is already a class that has some of the code you require, then it is possible to derive your new class from the already existing code.

This concept allows you to reuse the fields and methods of the existing class with out having to rewrite the code in a new class. In this scenario the existing class is called the super class and the derived class is called the subclass.

In Java language an interface can be defined as a contract between objects on how to communicate with each other. Interfaces play a vital role when it comes to the concept of inheritance.

An interface defines the methods, a deriving class(subclass) should use. But the implementation of the methods is totally up to the subclass.
What is Next ?

The next section explains about Objects and classes in Java programming. At the end of the session you will be able to get a clear picture as to what are objects and what are classes in java.


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