Question

I have searched for this, but unfortunately, I don’t get the correct answer.

class Helper {
    public static <T> T[] toArray(List<T> list) {
        T[] array = (T[]) new Object[list.size()];
        for (int i = 0; i < list.size(); i++) {
            array[i] = list.get(i);
        }
        return array;
    }
}

Test it:

public static void main(String[] args) {
    List<String> list = new ArrayList<String>();
    list.add("abc");
    String[] array = toArray(list);
    System.out.println(array);
}

But there is an error thrown:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;
at test.Helper.main(Helper.java:30)

How to solve this?

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UPDATE

I want this method, because sometimes, the type in my code is too long:

newEntries.toArray(new IClasspathEntry[0])

I’d hope to call:

toArray(newEntries)

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FINALLY

It seems impossible to create such a method, thank you all very much!

Answer 1

You can just call list.toArray(T[] array) and not have to worry about implementing it yourself, but as aioobe said, you can’t create an array of a generic type due to type erasure. If you need that type back, you need to create a typed instance yourself and pass it in.