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By extending class Vector, Java’s designers were able to create class Stack quickly. What are
the negative aspects of this use of inheritance, particularly for class Stack?
One problem is that Stack is a class, not an interface. This diverges from the design of the collection framework, where your noun is typically represented as an interface (e.g., List, Tree, Set, etc.), and there are specific implementations (e.g., ArrayList, LinkedList). If Java could avoid backward compatibility, then a more proper design would be to have a Stack interface, then VectorStack as an implementation.
A second problem is that Stack is now bound to Vector, which is generally avoided in favour of ArrayLists and the like.
A third problem is that you cannot easily provide your own stack implementation, and that stacks support very non-stack operations like getting an element from a specific index, including the potential for index exceptions. As a user, you may also have to know if the top of the stack is at index 0 or at index n. The interface also exposes implementation details such as capacity.
Of all the decisions in the original Java class library, I consider this one of the more peculiar ones. I doubt that Aggregation would have been much more expensive than inheritance.