Here, I wondered about how to implement Collection#toArray(T[] array) properly. I was mostly annoyed that array.getClass().getComponentType() is of type Class<?> and not Class<? extends T> as I would have expected.
Therefore, I coded these three functions:
@SuppressWarnings("unchecked") static <T> Class<? extends T> classOf(T obj) {
return (Class<? extends T>) obj.getClass();
}
@SuppressWarnings("unchecked") static <T> Class<? extends T> classOf(T[] array) {
return (Class<? extends T>) array.getClass().getComponentType();
}
@SuppressWarnings("unchecked") static <T> T[] newArray(Class<T> clazz, int size) {
return (T[]) Array.newInstance(clazz, size);
}
And then, my toArray implementation looks like:
public <T> T[] toArray(T[] array) {
int size = size();
if (array.length < size) {
array = newArray(classOf(array), size);
} else if (array.length > size) {
array[size] = null;
}
int i = 0;
for (E e : this) {
array[i] = classOf(array).cast(e);
i++;
}
return array;
}
What I wonder about now is:
Are these 3 helper functions always safe? Esp., is the cast always safe?
Why aren't these functions already in Java?
Also see this very related questions: T obj for a generic type T. The type of obj.getClass() is Class<?> and not Class<? extends T>. Why?