Inheritance in Static Methods

Question

Why does the below code print "Main"?

public class Main
{
    public static void method()
    {
        System.out.println("Main");
    }

    public static void main(String[] args)
    {
        Main m = new SubMain();
        m.method();
    }
}

class SubMain extends Main
{
    public static void method()
    {
        System.out.println("SubMain");
    }
}

At runtime, m is pointing to an instance of Submain, so it should conceptually print "SubMain".

Answer 1

Static methods are resolved on the compile-time type of the variable. m is of type Main, so the method in Main is called.

If you change it to SubMain m ..., then the method on SubMain will be called.

Answer 2

It is because static methods are not polymorphic. Moreover static method should be invoked not by object but using the class, i.e. Main.method() or SubMain.method(). When you are calling m.method() java actually calls Main.method() because m is of type Main.

If you want to enjoy polymorphism do not use static methods.

Answer 3

Eclipse gives me this sort of warning when I try to do this sort of thing:

The static method XXX() from the type XXX should be accessed in a static way

Static methods do not take part in inheritance. The variable is of type Main, so the compiler resolved your function call to Main.method().

For added fun, try setting m to null.