Is there a way to guarantee an interface extends a class in Java?

Question

Suppose I have the following situation:

public abstract class Vehicle {
  public void turnOn() { ... }
}

public interface Flier {
  public void fly();
}
         


        

Answer 1

You could rearrange your classes and interfaces like this:

public interface IVehicle {
  public void turnOn();
}

public abstract class Vehicle implements IVehicle {
  public void turnOn() { ... }
}

public interface Flier extends IVehicle {
  public void fly();
}

This way all implementations of Flier are guaranteed to implement the protocol of a vehicle, namely IVehicle.