posted 16 years ago
There's no actual term "null interface." What you might be referring to is a marker interface, which is indeed an interface defined with no actual methods to implement.
One of the most well-known examples is Serializable. When you implement Serializable, you do not have to actually implement any methods; you are simply telling the JVM that this class is allowed to be serialized. Another example is the Java 5 addition RandomAccess, which is implemented by ArrayList (and other classes) to signify that it provides effecient ( O(1) ) access to its elements.
So that's all there is to "null" interfaces.
-Matt
Current CS undergrad
SCJP 5.0