In this, 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 the main method. 

The requirements for Java Hello World Example are:

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 How to Set Path in Java
  • Create the java program
  • Compile and run the java program

Creating Java Hello World Example


    class Simple{  
        public static void main(String args[]){  
         System.out.println("Hello Java");  
        }  
    }


Save this file as Simple.java

To compile: javac Simple.java

To execute: java Simple


Compilation Flow:

When we compile Java Program using javac tool, java compiler converts the source code into byte code.

Java Compilation Flow


Parameters used in First Java Program:

In this we learn the meaning of class, public, static, void, main, Strings[], System.out.println() which are used in the First Java Program.

  • 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 the static method. The main advantage of this is that there is no need to create an object to invoke the static method. The main method is executed by the JVM, so it doesn't require to create an object to invoke the main method. So it save the memory.
  • void is the return type of the method. It means it doesn't return any value.
  • main represents the starting point of the program.
  • String[] args is used for command line argument. We will learn it later.
  • System.out.println() is used to print statement. Here, System is a class, out is the object of the PrintStream class, println() is hte method of PrintStream class. 

Different ways of writing Java Programs

There are many ways to write a java program which are given below:

1) By changing the sequence of the modifiers, method prototype is not changed in Java: -

The simple code of the main method.

static public void main(String args[])

2) The subscript notation in Java array can be used after type, before the variable or after the variable.
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 the main method by passing 3 ellipses (dots).

The simple code of using var-args in the main method.

public static void main(String... args)


4) Having a semicolon at the end of class is optional in Java.

    class A{  
    static public void main(String... args){  
    System.out.println("hello java4");  
    }  
    };


Valid java main method signature

public static void main(String[] args)  
public static void main(String []args)  
public static void main(String args[])  
public static void main(String... args)  
static public void main(String[] args)  
public static final void main(String[] args)  
final public static void main(String[] args)  
final strictfp public static void main(String[] args)

Invalid java main method signature

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


Resolving an error "javac is not recognized as an internal or external command"?

If there occurs a problem like "javac is not recognized as an internal or external command" then you need to set path. Since DOS doesn't know javac or java, we need to set path. The path is not required in such a case if you save your program inside the JDK/bin directory. However, it is an excellent approach to set the path. Click here for How to set path in java.