Chapter: Interfaces

Create an abstract class with no methods. Derive a class and add a method. create a static method that takes a reference to the base class, downcasts it to the derived class, and calls the method.

package chapter.interfaces;

abstract class Base {
}

class Sub extends Base {
    public void foo() {
        System.out.println("Sub foo");
    }
}

public class Exercise4 {
    private static void bar(Base b) {
        ((Sub) b).foo();
    }

    public static void main(String[] args) {
        bar(new Sub());
    }
}