Interfaces allow for two features:
1. It creates an IS-A relationship with the implementing class (or extending interface)
2. It gives a contract for the methods that will be present in the implementing class (or extending interface)
If the Interface is empty, it effectively only gives you only #1 above. I haven't used this variant in my code at all.
However, there are interfaces such as Serializable that tells the JVM that an Object can be serialized. This interface has no methods, but it establishes an IS-A relationship nevertheless.
as already mentioned... that is_a relationship can be very important in your development--i have an interface for on of my games "displayable" do if it is implemented in the object, i know that it supports writing to the screen... besides that you can extend once... and implement as many as you want in each object.
Out on HF and heard nobody, but didn't call CQ? Nobody heard you either. 73 de N7GH