TechnoLanguages: Simple Program of Java

In this page, we will learn how to write the simple program of java. We can write a simple hello java program easily after installing the JDK.

To create a simple java program, you need to create a class that contains main method. Let's understand the requirement first.

Requirement for Hello Java Example

For executing any java program, you need to

install the JDK if you don't have installed it, download the JDK and install it.
set path of the jdk/bin directory. http://www.javatpoint.com/how-to-set-path-in-java
create the java program
compile and run the java program

Understanding first java program

Let's see what is the meaning of class, public, static, void, main, String[], System.out.println().

class keyword is used to declare a class in java.
public keyword is an access modifier which represents visibility, it means it is visible to all.
static is a keyword, if we declare any method as static, it is known as static method. The core advantage of static method is that there is no need to create object to invoke the static method. The main method is executed by the JVM, so it doesn't require to create object to invoke the main method. So it saves memory.
void is the return type of the method, it means it doesn't return any value.
main represents startup of the program.
String[] args is used for command line argument. We will learn it later.
System.out.println() is used print statement. We will learn about the internal working of System.out.println statement later.

How many ways can we write a java program

There are many ways to write a java program. The modifications that can be done in a java program are given below:

1) By changing sequence of the modifiers, method prototype is not changed.

Let's see the simple code of main method.

2) subscript notation in java array can be used after type, before variable or after variable.

Let's see the different codes to write the main method.

public static void main(String[] args)  
public static void main(String []args)  
public static void main(String args[])  

3) You can provide var-args support to main method by passing 3 ellipses (dots)

Let's see the simple code of using var-args in main method. We will learn about var-args later in Java New Features chapter.

4) Having semicolon at the end of class in java is optional.
Let's see the simple code.

save this file as Simple.java

To compile and run the above program, go to your current directory first; my current directory is c:\new .

Write here:

To compile:

javac Simple.java

To execute:

java Simple

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