gistfile1.java

interface Foo {
  public void update();
}

class abstract Bar {
  
  private List<Foo> listeners;

  ...

  public void fireEvent() {
    for (Foo listener : listeners) {
      listener.update();
    }
  }
}

class Baz extends Bar {
  public void doSomething() {
    this.fireEvent();
  }
}