As in java every object is extended from the Object class. Can any one tell me whether interfaces are also extended from Object or not, if not then why?
and what will be the superclass of interfaces??
No, interfaces do not extend Object. Interfaces can only extend other interfaces, not regular classes. Since Object is a class (not an interface), interfaces cannot extend Object.
But you can't create an instance of an interface. You can only create instances of classes. And since Object is the superclass of all classes, you know that when you have an object, it always has the methods that are available in class Object.
If your interface doesn't explicitly extend another interface, then your interface is itself at the top of the inheritance hierarchy. Interfaces don't have an implicit top-level interface in the same way that all classes implicitly extend class Object.