Question

I have tried to google this one, but I can’t find an acceptable answer. Is interface inconsistency, when you make a class implement 2 or more interfaces which are incompatable with each other? For ex:

public interface Lion()
{
    public void eat();
}

public interface Tiger()
{
    public void eat();
}

public class Liger implements Lion, Tiger
{
    public void eat(); //Problem: How does it eat? Like a lion or tiger?
}

Am I correct or way off base?

Answer 1

In Java, you are guaranteed that an two interface methods which compile to the same function return the same “type”…. Thus, in this context, interface inconsistency can refer to :

1. When you implement 2 methods that implement the exact same function, with different side-effects , or diferent underlying assumptions/algorithms that are not expressible in the method signature… i.e. two methods that “look” the same but that “do” different conceptual tasks.

2. There is also the (non-java specific) GUI connotation, wherein the user experience is confusing, with similar components being utilized for different tasks (or vice-verse, the same task being triggered by different GUI components).

The solution to 1 is to have a more expressive interface, or more precise function names (to exemplify a more sophisticated interface: maybe the Lion and Tiger should provide an Eater object, which is capable of eating in one or more different ways).