Thread: My doubt may be stupid

Hi!

I having a stupid doubt....Sorry for asking ths....

when we creating Interface or abstract class we defining method,after that
we extends ths interface or abstract class to other class.....
for eg :

 interface testInteface{
public void calculation();
}

my doubt is after we extends the interface again we are creating method like

class exampleClass implements testInteface{
public void calculation() {          // this called overriding method from interface... but it seems like we creating                                                                          
                                                     method once again what is the advantage of having interface  
}
}

hope u understand my doubt,I don't have a basic knowledge of java,....i am having this doubt from the begging
help me out.............

Thanks,

Kalees

In a sense, yes you are over-riding the method. However, that's the point. The method defined in the interface does nothing, but it allows someone who wants to use that interface to know what they can expect to give as input and what to expect as output.

Ex: say we have an interface that's called Drivable, which inside has the methods turnLeft and turnRight. Then, we have several classes that implement Drivable: Civic, Bike, Fararri. The Drivable interface methods by themselves don't mean anything (makes sense, what are you driving?), but in each implementing class, they MUST implement the turnLeft/turnRight methods to be Drivable.

The same idea applies to abstract classes. Take the abstract class Shape. Inside, let's pretend we have an abstract method called area. What is the area of a shape? It's inherently undefined. However, if we have a class Square that inherits from Shape, it must implement the area method (or, be declared an abstract class, but that doesn't make much sense here).