The actual point to take away is that implements is ALWAYS preferred over extends on any questionable cases.
Extends binds two class files very closely and can cause some pretty hard to deal with code.
When I first "understood" OO programming I was extending EVERYTHING, but it turned my whole design into mush. Now I extend just the few things that clearly and obviously pass the "is-a" test and everything else is an interface...
Many many problems just stopped happening (Confusing multiple inheritance situations, time wasted refactoring hierarchies, the tendency to have "protected" variables then wonder why they are changing when you didn't change them in the current class, chaining requirements for constructors, figuring out how different inheritance-trees interact with each other, ...
It seems like every 3 years (for the last 20) I think I really "Get" programming and look back at the stupid things I did 3 years ago in shame... This was one of those instances (but from closer to 7 years ago at this point)
