Valid variants of main() in Java

Below are different variants of main() that are valid.

1. Default prototype: Below is the most common way to write main() in Java.

   class Test 
   {
       public static void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

   Meaning of the main Syntax:

   public:  JVM can execute the method from anywhere.
   static:  Main method can be called without object.
   void:    The main method doesn't return anything.
   main():  Name configured in the JVM.
   String[]: Accepts the command line arguments. 

2. Order of Modifiers: We can swap positions of static and public in main().

   class Test
   {
       static public void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

3. Variants of String array arguments: We can place square brackets at different positions and we can use varargs (…) for string parameter.

   class Test
   {
       public static void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

   class Test
   {
       public static void main(String []args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

   class Test
   {
       public static void main(String args[])
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

   class Test
   {
       public static void main(String...args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

4. Final Modifier String argument: We can make String args[] as final.

   class Test
   {
       public static void main(final String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

5. Final Modifier to static main method: We can make main() as final.

   class Test
   {
       public final static void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

6. synchronized keyword to static main method: We can make main() synchronized.

   class Test
   {
       public synchronized static void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

7. strictfp keyword to static main method: strictfp can be used to restrict floating point calculations.

   class Test
   {
       public strictfp static void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }
   

   Output:

   Main Method

8. Combinations of all above keyword to static main method:

   class Test
   {
       final static synchronized strictfp static void main(String[] args)
       {
           System.out.println("Main Method");
       }
   }

   Output:

   Main Method

9. Overloading Main method: We can overload main() with different types of parameters.

   class Test
   {
       public static void main(String[] args)
       {
           System.out.println("Main Method String Array");
       }
       public static void main(int[] args)
       {
           System.out.println("Main Method int Array");
       }
   }

   Output:

   Main Method String Array

10. Inheritance of Main method: JVM Executes the main() without any errors.

    class A
    {
        public static void main(String[] args)
        {
            System.out.println("Main Method Parent");
        }
    }
    
    class B extends A
    {
    
    }

    Two class files, A.class and B.class are generated by compiler. When we execute any of the two .class, JVM executes with no error.

    O/P: Java A
    Main Method Parent
    O/P: Java B
    Main Method Parent

11. Method Hiding of main(), but not Overriding: Since main() is static, derived class main() hides the base class main. (See Shadowing of static functions for details.)

    class A
    {
        public static void main(String[] args)
        {
            System.out.println("Main Method Parent");
        }
    }
    class B extends A
    {
        public static void main(String[] args)
        {
            System.out.println("Main Method Child");
        }
    }
    

    Two classes, A.class and B.class are generated by Java Compiler javac. When we execute both the .class, JVM executes with no error.

    O/P: Java A
    Main Method Parent
    O/P: Java B
    Main Method Child

This article is contributed by Mahesh. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above