Creating an array of generic stacks

Question

Stack<E>[] stacks = {new Stack<Bed>(), new Stack<Bookshelves>(), new Stack<Chair>(), new Stack<Desk>(), new Stack<Table>()};

For class I had to make my own Stack class that takes in whatever object I specify. As per specification, I have to put all the Stacks into an array.

But, when I try to create an Array of Stacks, I get a "cannot find symbol: class E" error.

What can I do to create an array of generic stacks?

You cannot create an array of generics. But what would you want to do with it if you could? — Oliver Charlesworth
– Oliver Charlesworth, Commented Mar 25, 2012 at 22:15
You're almost certainly better off creating a List of Stacks. (Although for your particular case, I frankly think you shouldn't create an array or list at all, but should keep the lists of the different types as explicit, separate variables.) — Louis Wasserman
– Louis Wasserman, Commented Mar 25, 2012 at 22:32

Paul · Accepted Answer · 2012-03-25 22:17:22Z

Generic type declarations such as <E> only work when you are defining a class, like

public class Stack<E>{ // etc. }

To create an array of Stacks like you are doing, you could either use the wildcard generic:

Stack<?>[] stacks = {new Stack<Bed>(), new Stack<Bookshelves>(), new Stack<Chair>(), new Stack<Desk>(), new Stack<Table>()};

Or if all your objects inside the stacks share a common inheritance, you could narrow down the wildcard with something like

Stack<? extends Furniture>[] stacks = {new Stack<Bed>(), new Stack<Bookshelves>(), new Stack<Chair>(), new Stack<Desk>(), new Stack<Table>()};

Stack<?>[] works, but Stack<? extends Furniture>[] doesn't because you cannot create generic arrays, at least not with that nice short syntax :/

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