The 'instanceof' operator behaves differently for interfaces and classes

Question

I would like to know regarding following behavior of instanceof operator in Java.

interface C {}

class B {}

public class A {
    public static         


        

Answer 1

By using the final modifier in the class declaration below, it is guaranteed that there couldn't be a subclass of Test, which may implement the interface Foobar. In this case, it is obvious that Test and Foobar are not compatible with each other:

public final class Test {

    public static void main(String[] args) {
        Test test = new Test();
        System.out.println(test instanceof Foobar); // Compiler error: incompatible types
    }
}

interface Foobar {
}

Otherwise, if Test is not declared final, it might be possible that a subclass of Test implements the interface. And that's why the compiler would allow the statement test instanceof Foobar in this case.