为什么不能实例化抽象类和接口？

Question

Why are we not able to create the instance of the abstract class and interface? Means, abstract class and interface cannot be instaniated and only can be implemented by the Class.

Answer 1

I like this answer :

An abstract class is a special kind of class that cannot be instantiated. So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.

An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments.

Answer 2

In a normal situation, this is because to create an instance of a class requires that a block of memory is set aside for that instance to reside in. An abstract class or an interface does not contain all of the information required to create an instance of it. It only contains the information needed to describe the class.

Trying to create an instance of an abstract class or an interface is like spending money on a box of bricks, but with nothing inside of it. You only have the outside, nothing inside.