Question

You must declared Main class which contains 'main' method, which is entry point of program execution.in java

Answer 1

Exactly as the error message says. You need a class that is called Main and it must have a method with the signature public static void main(String[] args).

If you start a new project in OnlineGDB and select the language Java (in the top-right corner), this is exactly what will be provided to you.

I'll copy it here, just for reference:

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