Listener Interface implementation questions

Question

Dear all experts,
I am getting a bit confused of the "standard" way of implementing listener interfaces.
I found that there are 3 general methods:
1) create an extra class implementing the interface.
2) implement the interface as an inner class
3) using the existing class to implement the inferface :
eg:
public class oneofmyclass implement FocusListener
public oneofmyclass()
constructor....
all my other methods.........
the interface methods......
Why there are so many ways to do it?
what's the differences/benefits of each??
Thx

Answer 1

I am getting a bit confused of the "standard" way of implementing listener interfaces.
I found that there are 3 general methods:
1) create an extra class implementing the interface.
2) implement the interface as an inner class
3) using the existing class to implement the inferfaceThere isn't much difference between 1) and 2). The first alternative creates a named inner class
(that implements the listener interface) while the second creates an anonymous class using that
listener interface. Alternative 3) exposes the interface to the outer world, i.e. your class may be
attached to some listener list (in some observable) it really wasn't meant for.
I prefer 1) or 2) If the actual code for the listener is small I use 2), otherwise I use 1) but that's
just for readability reasons. I almost never use 3) because I don't want my class to be hooked
up to any observable it wasn't designed for.
kind regards,
Jos