[java] How to create a generic array?

I don't understand the connection between generics and arrays.

I can create array reference with generic type:

private E[] elements; //GOOD

But can't create array object with generic type:

elements = new E[10]; //ERROR

But it works:

elements = (E[]) new Object[10]; //GOOD

checked :

public Constructor(Class<E> c, int length) {

    elements = (E[]) Array.newInstance(c, length);
}

or unchecked :

public Constructor(int s) {
    elements = new Object[s];
}

Problem is that while runtime generic type is erased so new E[10] would be equivalent to new Object[10].

This would be dangerous because it would be possible to put in array other data than of E type. That is why you need to explicitly say that type you want by either

• creating Object array and cast it to E[] array, or
• useing Array.newInstance(Class componentType, int length) to create real instance of array of type passed in componentType argiment.

Here is the implementation of LinkedList<T>#toArray(T[]):

public <T> T[] toArray(T[] a) {
    if (a.length < size)
        a = (T[])java.lang.reflect.Array.newInstance(
                            a.getClass().getComponentType(), size);
    int i = 0;
    Object[] result = a;
    for (Node<E> x = first; x != null; x = x.next)
        result[i++] = x.item;

    if (a.length > size)
        a[size] = null;

    return a;
}

In short, you could only create generic arrays through Array.newInstance(Class, int) where int is the size of the array.