Question

class NewClass{
    public static void main(String a){
        System.out.print("Hello");
    }
}

When I’m trying to execute above code, then it shows an error: main method not found. When I changed the signature to

public static void main(String... a)

or

public static void main(String a[])

Then it works. My question is how many different ways we can write legal main method signature? And what does the String... version mean?

Answer 1

Simply because that’s the requirement of Java.

A main method/entry point to a program must be a method declared as public static void main(String[] args). Your method that was declared with a String parameter was similar but not compatible.

An array is not the same as a single String – if someone invoked Java with three command-line parameters, the JVM would create a three-element string array, and then how would it pass this into your method that only takes a single string?

So in that case you were trying to launch a Java program based on a class that did not have an main method to act as an entry point.

(The reason why String... works is because this is syntactic sugar for an array parameter, and compiles down to a method with the same signature.)