Foo.java

public abstract class Foo {
    private Foo() {}

    public abstract void overrideMePlease();

    public static class Bar extends Foo {
        @Override
        public void overrideMePlease() {
            System.out.print("overriden in " + this.getClass().getSimpleName());
        }
    }

    public static class Baz extends Foo {
        @Override
        public void overrideMePlease() {
            System.out.print("also overriden in " + this.getClass().getSimpleName());

        }
    }
}