Understanding Hello World Java Program

Now you are familiar with the Java program. In the last lesson you learned how to compile and run the Java program. Before start hard programming in Java, its necessary to understand each and every part of the program. Lets understand the meaning of  public, class, main, String[] args, System.out, and so on.

Class Declaration:

Class is the building block in Java, each and every methods & variable exists within the class or object. (instance of program is called object ). The public word specifies the accessibility of the class. The visibility of the class or function can be public, private, etc. The following code declares a new class "HelloWorld" with the public accessibility:

public class HelloWorld { 

The main Method: 

The main method is the entry point in the Java program and java program can't run without main method. JVM calls the main method of the class. This method is always first thing that is executed in a java program. Here is the main method:

public static void main(String[] args) {

......
.....

}

{ and is used to start the beginning of main block and } ends the main block. Every thing in the main block is executed by the JVM.

The code:

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

prints the "Hello World" on the console. The above line calls the println method of System.out class.

The keyword static:

The keyword static indicates that the method is a class method, which can be called without the requirement to instantiate an object of the class. This is used by the Java interpreter to launch the program by invoking the main method of the class identified in the command to start the program.