Why is interface required

Question

Friends can u please explain me why Interface is required.I read few explanation and I am having problems understanding it .
thanks
Manohar

Answer 1

For example you can specify interface like this:
public interface Namer {
public String getName();
Then you can implement class with code like this:
public void printName(Namer nm){
System.out.println(nm.getName());
Then you can tell your friends 1,2,3:
1 implement for me Namer to take name from net
2 implement for me Namer to take name from dastabase
3 implement for me Namer to take name from flat file
And when they provide you with this implementation, every class which implements Namer interface can be passed to your printName method.
This is very syntetic example. In short: interfaces provides some abstraction, they allow you to specify inter-object communication abstracting from implementation details. In my opinion greatest set of interfaces is JDBC.