public class ListImpl extends List

is no better than

public class List : IList

And for the exact same reason.

Always have your class name give a meaningful description of how the class implements the interface. Sometimes the implementation affects scalability like in the list example. Sometimes the implementation requires resources like Internet access. Sometimes the implementation supports high availability or multi-user access or synchronization, etc. There’s always a meaningful adjective to modify a class that implements one or more interfaces.

public class List : IList

instead of

public class LinkedList : IList
public class ArrayList : IList
public class HashList : IList

Even the .NET common class authors fell into this trap. A class name should NEVER be the name of the interface with just the “I” removed. The class name should always tell the user how the class differs from other possible implementations of the interface(s). I vote for dropping the stupid “I” for that reason alone.

Also, when I use intelisense, I want to group things by functional area, not whether it’s a class or interface. I never think, “I need an interface, not a class.” I always think, “I need something that does X”.

~Lee