when u want behavior of interface then u can implement that
inteface with any other class and after instantiate that
class u can get behavior of that interfce because by default
methods in interface are abstract,  
But in case of abstract class u can not create object of
abstract class means you can not instantiate abstact class
but after extending or by creating base class pointer ,using
dynamic method dispatch u can get behavior of abstract class

If there are multiple objects which use common methods and 
different implementaion of methods We use Abstract class.

If multiple objects use different implementation of methods 
for every object we use interface.

If we have more than two classes with same method names but 
their implementation is different.we can go for interface.
Example: JDBC API Interfaces. Every data base vender 
implements these interfaces with thier implementation code.

If we want to use some common method implementaions for 
multiple classes along with their own implementation we can 
go for abstract class.

Example:Servlet API:
HttpServlet is an abstract class in which init() is 
implemented used by every servlet that extends.Every 
servlet implement their own service method.

Interface:
Used for mutiple inheritance.

First i will explain u abstract Class:--------------
                                                    Suppose
u open the car-show room which having all companys car and
user want to by a car, but user not sure about the company,
means user requirement is a good car. So he will come in ur
show room and ask about the every company car so how u gonna
to do this task.

So how u start.

First of all every car having some common characteristic.
That is
a)Color of car
b)Shape of car
c)gear in car
d)Type of car
e)Price of car
..........................etc.

So what we are doing is actually we are writing a abstract
class that is called Car and then we summarized the common
properties of car.

                   Why this is required because if we not
summarized the common properties of car,for every car we
have to define these common properties.Hence for that we
declare once the all common aspect of the car and the let
user choose the choice according to him.

So in abstract class we are going to define only the method
not the body and let user to allow to define his own type of
car.

abstract class Car
{
//(very important)

// we are here defining only the method not body and if any
//method end with semicolon means it is abstract method and
//if any single method in the class is abstract then class
//must be abstract. but in abstract class //we can define
the concrete method(which is not abstract) //also
public void color();  
public void price();
public void types();

Class Bmw extends car
{
//here we are define the user requirement of the car that //
is bmw and we are defining the method with body also 
public void color()
{
System.out.println("color of car is red");
}
public void price()
{
System.out.println("price of car is......");
}
}
Public Tata extends car
{
public void color()
{
System.out.println("color of car is blue");
}
public void price()
{
System.out.println("price of car is......");
}
}

I think u gain some fact about abstract class.


Interface------------------java dont have multiple
inheritance concept........so java using multiple
inheritance by INTERFACE.

Actually interface is a set of rules....it rquired when u
want to achieve multiple inheritance .
The set of rules says
1)all method are by default public staic and abstract
2)All the variables are public static and final.

So for interface u have to implements
Example

Class Anjani implements ABC(means abc is interface)

{

}

For further assistance u may call me
Anjani Kumar Jha
09623154095
CDAC,PUNE