Why can't you instantiate an Interface or Abstract Class?
Instantiation Restrictions
An interface cannot normally be instantiated because it defines a contract rather than a complete concrete object implementation. An abstract class cannot be instantiated because it may contain abstract operations whose behavior is intentionally incomplete. The runtime needs a concrete type with all required behavior defined before it can create a normal object. However, a reference of interface or abstract-class type can point to a concrete implementing or derived object.
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Interfaces represent contracts rather than directly constructible concrete objects.
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Abstract classes can contain incomplete behavior.
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Concrete subclasses provide the missing behavior.
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Interface and abstract-class references can still point to concrete objects.
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This supports abstraction and runtime polymorphism.
Follow-up Questions
- Can an abstract class have a constructor?
- Can an abstract class be fully implemented?
- Why can an interface reference point to an object?
- What is upcasting?