Array of a generic class

Question

I have a Box class which holds a value and I want to create an array of this class.

Box Class:

public class Box<T> {
    public T t;
    public Box(T t){ this.t = t; }
}

Test Class:

public class Test {
    public static void main(String[] args) {
        Box<Integer>[] arr = new Box<Integer>[10];
    }
}

Compiler says :

Cannot create a generic array of Box

I wonder that why we cant do that and how can I do that?

Answer 1

Java does not allow generic arrays.

You can find more info here: Java Generics FAQ.

For a quick fix, use List (or ArrayList) instead of Array.

List<Box<Integer>> arr = new ArrayList<Box<Integer>>();

Detailed explanation of the issue: Java theory and practice: Generics gotchas:

Answer 2

This used to work(generates a warning), should still do what you need:

 Box<Integer> arr = (Box<Integer>[]) new Box[10];

Answer 3

No, you can't because of type erasure, there are two possible workarounds:

• use an ArrayList<Box<Integer>>
• use reflection (but you will have warnings) through java.lang.reflect.Array.newInstance(clazz, length)

Answer 4

Box<Integer> arr = (Box<Integer>[])new Box<?>[10];