Interface vs Abstract class

[jose chiramal]

I would like to know when do we use Interface and when ABstract classes. I came across the following :

1.If you need to change your design make it an interface. Abstract classes provide default behavior. - what do these statements mean, what does behavior mean here?

[Rob Spoor]

Please do a search. This question has been asked dozens of times before. We even have an FAQ entry for it: http://faq.javaranch.com/java/InterfaceVsAbstractClass

[David Newton]

In fact, *you* asked it. And what exactly are you asking? What do *you* think "default behavior" is--based on the results of when you asked this question here?

[Jim Hoglund]

What still bothers you about abstract classes and interfaces and their use?

Jim ... ...