I know, we can not instantiate either an interface or an abstract class in java except using anonymous class method but what is the reason behind it?
You can't instantiate an interface or an abstract class because it would defy the object oriented model.
Interfaces represent contracts - the promise that the implementer of an interface will be able to do all these things, fulfill the contract.
Abstract classes are a similar idea, in that they represent an unfulfilled contract, a promise to be able to do things, except unlike interfaces they have some of their functions or fields defined but need filling in before they can used.
Simply, in a good object oriented program, you should never want to instantiate an abstract class or interface. If you do, the design is probably wrong.
(Anonymous classes are actually non-abstract instantiations, just that they don't need to be given a name, so they appear to be 'raw interfaces' but they're actually an implementation of the interface that has no name. That's my understanding, at least.)
Here is a basic explanation without deeper concept.
Interface
has no method implemented, so there is no purpose to instantiate it as 'nothing' will happen when invoke a methodAbstract
class can have abstract
method declaration, which is like a interface method with no implementation.You can't instantiate interfaces or abstract classes because some of their methods might not have any definitions.
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