Java interface abuse

WithInterfaceAbuse.java

// Fun trick I've been playing with to replace abstract classes with empty java interfaces.

public class BaseClass {
  // stuff ...
}

public class PurpleClass extends BaseClass implements Controller.IsPurple {
  // methods ...
}

public class OrangeClass extends BaseClass {
  // methods ...
}

public class Controller {
  public interface IsPurple {}

  private BaseClass myClass;

  public Controller(BaseClass baseClass) {
    this.myClass = baseClass;
  }

  public void timeToDoSomething() {
    if(this.myClass instanceof IsPurple) {
      doSpecialThingHere();
    }
    else {
      doNotSoSpecialThingHere();
    }
  }
}

WithoutInterfaceAbuse.java

// More conventional, but more verbose approach to the same thing. Also, this approach means that
// the controller needs to know about the implementation details of BaseClass.

public abstract class BaseClass {
  public abstract boolean isPurple();
}

public class PurpleClass extends BaseClass {
  public boolean isPurple() {
    return true;
  }
}

public class OrangeClass extends BaseClass {
  public boolean isPurple() {
    return false;
  }
}

public class Controller {
  private BaseClass myClass;

  public Controller(BaseClass baseClass) {
    this.myClass = baseClass;
  }

  public void timeToDoSomething() {
    if(this.myClass.isPurple()) {
      doSpecialThingHere();
    }
    else {
      doNotSoSpecialThingHere();
    }
  }
}