Valid variants of main() in Java

The main method is the starting point for executing Java code. A runtime exception will be thrown if the JVM cannot locate a main method during runtime. In other words, if no main method is present in the Java code, the JVM will report an error at runtime.

The public access modifier in the main() method enables the JVM to execute the method from anywhere in the program.
The static keyword in the main() method declaration allows the method to be called without creating an object of the class.
The void return type specifies that the main() method does not return any value.
The name of the main() method is configured by the JVM, and it must always be named main().
The String[] parameter in the main() method allows the program to accept command-line arguments passed to the program when executed.
The name of the String array parameter is typically args, which refers to the array of String objects containing the command-line arguments.

Although the syntax of Java's main() method is generally strict, some minor modifications are allowed. These modifications do not result in a runtime exception. As a result, there are various valid variants of the main() method in Java. Understanding these variants is essential as they allow developers to modify the standard syntax slightly to suit their specific needs.

Default prototype

The following is the standard and widely accepted way to write Java's main() method.

Filename: Computer.java

class Computer
{
	public static void main(String[] args)
	{
		System.out.println("Welcome")
	}
}

Output:

Welcome

Order of Modifiers

The static and public modifiers in the main() method declaration can be interchanged without affecting the program's behavior.

Filename: Computer.java

class Computer
{
	static public void main(String[] args)
	{
		System.out.println("Welcome");
	}
}

Output:

Welcome

Variants of String array arguments

In Java, it is possible to place the square brackets at different positions when declaring the String parameter in the main() method.

Filename: Computer.java

class Computer
{
	public static void main(String[] args)
	{
		System.out.println("Welcome");
	}
}

Output:

Welcome

Filename: Computer.java

class Computer
{
	public static void main(String []args)
	{
		System.out.println("Welcome");
	}
}

Output:

Welcome

Filename: Computer.java

class Computer
{
	public static void main(String args[])
	{
		System.out.println("Welcome");
	}
}

Output:

Welcome

Args or anything

In the main() method in Java, you can use any valid Java identifier instead of args, such as your name, company name, or any other word or phrase that follows the rules for Java identifiers.

Filename: Computer.java

class Computer{
	public static void main(String[] HelloWorld){
			System.out.println("Welcome");
	}
}

Output:

Welcome

Var-args instead of String array

In Java, the main() method can be declared with a variable-length argument parameter (varargs) instead of a String array. It provides more flexibility in handling command-line arguments.

In Java, if the String parameter in the main() method is a one-dimensional array, you can use a varargs parameter (denoted by three dots ... instead of square brackets []) as a replacement.

Filename: MainMethodDemo.java

// The Java program is used to demonstrate the usage of varargs in the main method
public class MainMethodDemo {
public static void main(String... args) {
// printing the number of arguments passed
System.out.println("Number of arguments: " + args.length);
// printing each argument passed
for (String arg : args) {
System.out.println(arg);
        }
   }
}

Output:

Number of arguments: 0

The final Modifier String argument

In Java, it is possible to declare the String[] args parameter in the main() method as final, ensuring that the parameter's value cannot be changed.

Filename: MainMethodDemo.java

// The program demonstrates using the final keyword in the main method and iterating through the arguments passed to it.
public class MainMethodDemo {
// Declaring the main method with the final keyword
public static void main(final String[] args) {
System.out.println("Arguments:");
// Iterating through the arguments and printing them
for (final String arg : args) {
System.out.println(arg);
}
// args[0] = "new value";
}
}

Output:

Arguments:

Final main method

In Java, the final keyword can be applied to the main() method to prevent the method from being overridden in any subclass. It is possible to declare the main() method with the final keyword, which does not affect the execution of the program or cause any errors.

Filename: DemoExample.java

// Define a class named DemoExample
class DemoExample {
    
    // Define a final, public, static method named main with a String[] parameter
    final public static void main(String[] args) {
        System.out.println("It is a final main method");
    }
}

Output:

It is a final main method

Synchronized Keyword to Static Main Method

It is possible to declare the main() method synchronized in Java.

Filename: ComputerDemo.java

// The program demonstrates synchronized keywords with the main method in Java.
public class ComputerDemo {
// Declaring main method as synchronized
public static synchronized void main(String[] args) {
System.out.println("Synchronized Main Method");
}
}

Output:

Synchronized Main Method

strictfp keyword to the static main method

In Java, the strictfp keyword ensures consistent floating-point arithmetic across different platforms.

Filename: DemoStrictfp.java

// The is a Java program to demonstrate using the "strictfp" keyword with the main() method.
public class DemoStrictfp {
// Declaring the main() method as final and strictfp
final strictfp public static void main(String[] args) {
    
    // Using strictfp to ensure consistent floating-point calculations across different platforms
    double x = 1.0 / 3.0;
    double y = 2.0 / 3.0;
    System.out.println("x + y = " + (x + y));
}
}

Output:

x + y = 1.0

Overloading the Main method

We can overload the main() method in Java like any other method. Overloading means creating multiple methods with the same name but with different parameters. We can have any number of overloaded main() methods, but the one with the signature public static void main(String[] args) will be the entry point of the program.

Filename: MainOverloading.java

// Define a class called MainOverloading
class MainOverloading {
    // Define the main() method with String[] argument
    public static void main(String[] args) {
        System.out.println("It is the main() method with String[] argument");
    }

    // Define another version of the main() method with int argument
    public static void main(int arg) {
        System.out.println("It is the main() method with int argument");
    }

    // Define another version of the main() method with String argument
    public static void main(String arg) {
        System.out.println("It is the main() method with String argument");
    }
}

Output:

It is the main() method with String[] argument

Inheritance of the Main method

In Java, you can inherit the main() method from a superclass to a subclass as long as the method signature remains the same. If the subclass does not define its own main() method, it will inherit the main() method of its superclass. If the subclass does define its own main() method, it will override the main() method of its superclass. JVM Executes the main() without any errors.

Filename: Animal.java

// Animal class with a main method
class Animal {
public static void main(String[] args) {
System.out.println("It is the main method of Animal class");
    }
}

// Dog class inherits the main method from the Animal class and overrides it
class Dog extends Animal {
public static void main(String[] args) {
System.out.println("It is the main method of Dog class");
    }
}

Output:

It is the main method of the Animal class

Method Hiding of main(), but not Overriding

In Java, it's possible to "hide" the main method of a parent class in a child class using method hiding, but it's impossible to override it since it's a static method. Here's an example of a method hiding of main():

Filename: Animal.java

// It is the Animal class
class Animal {
    // It is the main method of the Animal class
    public static void main(String[] args) {
        System.out.println("It is the main method of Animal class");
    }
}
// It is the Dog class that extends the Animal class
class Dog extends Animal {
    // It is the main method of the Dog class
    public static void main(String[] args) {
        System.out.println("It is the main method of Dog class");
    }
    // It is the test method of the Dog class
    public static void test() {
        System.out.println("It is the test method of Dog class");
    }
}

Output:

It is the main method of the Animal class

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Valid variants of main() in Java

Default prototype

Order of Modifiers

Variants of String array arguments

Args or anything

Var-args instead of String array

The final Modifier String argument

Final main method

Synchronized Keyword to Static Main Method

strictfp keyword to the static main method

Overloading the Main method

Inheritance of the Main method

Method Hiding of main(), but not Overriding

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