Valid variants of main() in Java

11 May, 2022
We know that a Java code begins to execute from the main method. During runtime, if JVM can’t find any main method then we will get a runtime exception: No such Method Error:  
Main method not found in class, please define the main method as:
public static void main(String[] args) 
to avoid this problem there should be the main method. We also know that the java main method has a particular prototype, which looks like:  
public static void main(String[] args)
 Even though the above syntax(prototype) is very strict but some little changes are acceptable. This makes it not so strict that if we perform any change then we will get a runtime exception. We can do several allowed modification to our main method. The following Changes are acceptable. Let’s understand the different variants of main() that are valid. 
Default prototype: Below is the most common way to write main() in Java. 
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.
args:- the name of the String array is args.
 
Order of Modifiers: We can swap positions of static and public in main(). 
Java
//Java code to understand that The Order of Modifiers don't mattersclass Test{    static public void main(String[] args)    {        System.out.println("Main Method");    }}
Output:
Main Method
Variants of String array arguments: We can place square brackets at different positions for string parameter. 
Java
class Test{    public static void main(String[] args)    {        System.out.println("Main Method");    }}
Output:
Main Method
Java
class Test{    public static void main(String []args)    {        System.out.println("Main Method");    }}
Output:
Main Method
Java
class Test{    public static void main(String args[])    {        System.out.println("Main Method");    }}
Output:
Main Method
Args or anything: Instead of args we can write anything which is a valid java identifier. You can write anything here, you can write your name or company’s name or anything you want to write but it must follow the rule of being a java identifier. Example: 
Java
class Gfg{        public static void main(String[] geeksforgeeks){               System.out.println("Instead of args we have written geeksforgeeks");       }}
Output: 
Instead of args we have written geeksforgeeks
Var-args instead of String array: According to the rule whenever there is one dimensional array we can replace the array with var-arg parameter.So here we can change our string array using var-args. (the triple dots instead of []) Example: 
Java
//Java code-> using Var-Args instead of the array//please note these code may not run in gfg IDE, better run it on other IDEs e.g, eclipseclass Gfg{             final public static void main(String... args){        System.out.println("Var-args main method");    }}
Output: 
Var-args main method
Final Modifier String argument: We can make String args[] as final. 
Java
class Test{    public static void main(final String[] args)    {        System.out.println("Main Method");    }}
Output:
Main Method
Final main method: We can declare the main method with the final keyword.This cannot change the execution or give any error. Example:  
Java
//Java code having the final main method////please note these code may not run in gfg IDE, better run it on other IDEs e.g, eclipseclass Gfg{      final public static void main(String[] args){                   System.out.println("final main method");         }}
Output: 
final main method
synchronized keyword to static main method: We can make main() synchronized. 
Java
//Java code having Synchronized main method//please note these code may not run in gfg IDE, better run it on other IDEs e.g, eclipseclass Test{    public synchronized static void main(String[] args)    {        System.out.println("Main Method");    }}
Output:
Main Method
strictfp keyword to static main method: strictfp can be used to restrict floating point calculations.  
Java
//Java code-> using strictfp modifier in main method//please note these code may not run in gfg IDE, better run it on other IDEs e.g, eclipseclass Test{    public strictfp static void main(String[] args)    {        System.out.println("Main Method");    }}
Output:
Main Method
Combinations of all above keyword to static main method: So we can declare the java main method with the following modifiers:
Overloading Main method: We can overload main() with different types of parameters. 
Java
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
Inheritance of Main method: JVM Executes the main() without any errors. 
Java
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 a 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
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.) 
Java
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
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