Question

I have two sets of code in fist i have defined custom String class and trying to create instance of it while in second i have defined custom System class and trying to create instance of it.

This is neither an interview question nor homework, i just tried it after checking this

In this I am trying to create instance of String class i have defined and i got Exception in thread "main" java.lang.NoSuchMethodError: main

public class Test {
    public static void main(String[] args) throws Exception {
        String s = new String();
        java.lang.System.out.println("done");
    }
}

class String {
    public String() {
        java.lang.System.out.println("custom String");
    }
}

In this part i am trying to create instance of System class i have defined and it worked fine

public class Test {
    public static void main(String[] args) throws Exception {
        System s = new System();
        java.lang.System.out.println("done");
    }
}
class System {
    public System(){
        java.lang.System.out.println("custom System");
    }
}

Both String and System class are final, so why there is difference in behavior??

Answer 1

This is happening because your main is using your custom String class as argument type which is not matching with standard main method (entry point), which accepts java.lang.String[] as parameters; hence complaining.

Change your main to use java.lang.String class as:

       public static void main(java.lang.String[] args)