Basic Java Tutorials - First Java Program

Basic Java Tutorials For Selenium2.0 - WebDriver

- 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 of Java.

- This reference will take you through simple and practical approach while learning Java Programming language.

- This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to Java Programming language.

- Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware about what is a computer program and what is a computer programming language.

Java - Overview

- 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' Java platform (Java 1.0 [J2SE]).

- As of December 2008, the latest release of the Java Standard Edition is 6 (J2SE). With the advancement of Java and its widespread 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 of Java runtime system.
• Portable:Being architectural-neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler in 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.
• Multithreaded: With Java's multithreaded 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 being 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 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.

First Java Program :

Let's go over the Hello world program, which simply prints "Hello, World!" to the screen.
public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }

Description :

The first line defines a class called Main.

public class Main {

- In Java, every line of code that can actually run needs to be inside a class. This line declares a class named Main, which is public, that means that any other class can access it. This is not important for now, so don't worry. For now, we'll just write our code in a class called Main, and talk about objects later on.

- Notice that when we declare a public class, we must declare it inside a file with the same name (Main.java), otherwise we'll get an error when compiling.

The next line is:

public static void main(String[] args) {

- This is the entry point of our Java program. 

- The main method has to have this exact signature in order to be able to run our program.

• public again means that anyone can access it.
• static means that you can run this method without creating an instance of Main.
• void means that this method doesn't return any value.
• main is the name of the method.

The arguments we get inside the method are the arguments that we will get when running the program with parameters. It's an array of strings. We will use it in our next lesson, so don't worry if you don't understand it all now.

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

• System is a pre-defined class that Java provides us and it holds some useful methods and variables.
• out is a static variable within System that represents the output of your program (stdout).
• println is a method of out that can be used to print a line.