为什么java.util.Stack允许.add（int，E）？

Question

I am making a Deck class in Java. I only want the top Card to be accessible. I'm considering making Deck extend Stack , but Stack inherits from Vector , which has a method add(int, E) . Why does Stack allow you to add an element anywhere in it? Is there a way to remove/disallow calls to this method?

On the other hand, maybe I am completely thinking about this wrong. Is there a better way to make a Deck class? Should I make it extend and/or implement a different class and/or interface(s)?

Answer 1

I would use a Deque (also pronounced Deck) Stack and Vector were designed almost 20 years ago and Deque is a relatively new design (about 8 years)

Stack doesn't use an interface allowing it to hide methods which don't make sense for it's intended purpose.

Answer 2

Stack is an old class, just like Vector, that shouldn't be used anymore. You can't "disable" this method because, as you pointed out, Stack extends Vector, which has this method. And a subclass extends what a superclass can do, and does not restrict it. That's the principle of polymorphism. Since a Vector can di it, and since a STack is a Vector, it can do it as well.

Consider using Collections.asLifoQueue(new LinkedList());

Answer 3

Stack extending Vector is an example of bad design in the java libraries (see this from effective java).

as this item suggests, i'd avoid inheriting from a container and instead use composition