Part of the following post in orange-coding.blogspot.com: Enhancing (extending) a class using dynamic proxy classes in Java

AB.java

public interface AB extends A {
    String bar();
}

ABDecorator.java

public class ABDecorator implements AB {
    private final A delegate;
    public ABDecorator(A a) {
        this.delegate = a;
    }
    public String foo() {
        return this.delegate.foo();
    }
    public String bar() {
        return "bar ";
    }
}