Exact Use of Abstract Class And Interface

[Rajendra Prakash]

I googled what is Abstract class and interface.
I get Abstract class cannot be instantiated , which contains abstract and concreate methods.
If you want to implement some common or default behaviours we can use abstract class.
I get difference between abstract class and interface

What is the exact use of Abstract class and interface. when to use which.
I am new to java. though i read so many books i can't understand clearly.

[Christophe Verré]

That would be great if Google could easily find our FAQ.