Java Introduction

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]). Now it has became the one of the most popular computer programming language and is now being used by more than 2 billion devices.

  •          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.

 

Characteristics of Java:

  •           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 lightweight 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.

Java Basic Syntax

When we consider a Java program, it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what do class, object, methods and instance 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 describes 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.

·         Instance Variables – Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.

 

First Java Program:

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

/* This is my first java program.
   This will print 'Hello World' as the output */
public class MyFirstJavaProgram{
    public static void main(String[]args){
        System.out.println("Hello World");// prints 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 word's 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.

/*Here is another short example.
  Call this file "Example2.java".
*/
class Example2 {
    public static void main(String args[]) {
        int num; // this declares a variable called num
        num = 100; // this assigns num the value 100
        System.out.println("This is num: " + num);
        num = num * 2;
        System.out.print("The value of num * 2 is ");
        System.out.println(num);
    }
}

The output of the program is:

This is num: 100 
The value of num * 2 is 200

 

Java Basic Data Types