CODEWITHSUNDEEP
javagenerics
egelev
egelev

Reputation: 1205

How to specify two concrete type arguments for generic type with a single type parameter?

community. I have the following situation. I am using java collections, lets say the List interface for example. It is a generic interface with a type parameter E for its elements. In my case I know the type of the elements that are going to be inserted, but the problem is that two types of elements are going to be inserted. Lets say I have the class A and class B and they have nothing in common. The nearest common ancestor of A and B is the Object class. The types A and B are not defined by me, so I can not change the type hierarchies. If I define my list like this:

List<A> list = new ArrayList<>();

then only elements of type A will be allowed, and if I define it like this:

List<B> list = new ArrayList<>();

then only elements of type B will be allowed. Is there any way to do a logical OR ? How to specify that I want elements of type A or type B and nothing else ? Or the java way is to make:

List<Object> list = new ArrayList<>();

and to check the type on my own when I perform any list operations ?

Upvotes: 0

Views: 114

Answers (1)

Ray
Ray

Reputation: 3201

For your purpose, you'd need something like a union type, which Java doesn't provide. You gave the answer yourself: If you cannot modify the hierarchy, not even let A and B implement the same interface, then you'll have to use a List<Object> and do additional typechecks yourself.

Upvotes: 2

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