In simple (few)words i try to answer of What are these Listeners in java? I read it in J2CR(Java 2 The Complete Reference)book.
First we should understand event:- An Event is an object that describes a state change in a source. & A Source is an object that generates an event.
A source must register listeners in order for the listeners to receive notifications about a specific type of event.
Here is the general form:-
public void add Type Listener(TypeListener el)
here Type is the name of event & el is La reference to the event listener.
The listener is an object that is notified when an event occurs.
I not write all things here but
try these link:-
{
Listeners in Java}.
{
Listeners in Java}.