Object[] cannot be converted to Integer[]

Question

Converting a TreeSet object to an array using the toArray method, however I get the error:
Object[] cannot be converted to Integer[]

Here is the code:

public static void main (String[] args) {
    TreeSet elems = new TreeSet<Integer>();
    int[] elemsToAdd = {1,2,3,4};

    for(int i = 0; i < elemsToAdd.length; i++){
        elems.add(elemsToAdd[i]);
    }
    Integer[] elemsArray = elems.toArray(new Integer[elems.size()]);
 }

I've searched other threads for the answer, however all of them recommend to use the toArray method with an Integer array as an argument yet mine still throws an error.

Answer 1

That's due to your usage of raw type. When elems is defined as a raw TreeSet , elems.toArray returns an Object[] , not an Integer[] .

Change

TreeSet elems = new TreeSet<Integer>();

to

TreeSet<Integer> elems = new TreeSet<Integer>();

Answer 2

Erans Answer solves the error but I would also like to make my contribution

TreeSet<T> takes in any Object type, Making it TreeSet<Integer> Would allow you to put Integer values inside the TreeSet, Heres how you can define it

TreeSet<Integer> elems = new TreeSet<>();

You are using a regular loop that can be replaced with a for-each in your case working example is

for (int anElemsToAdd : elemsToAdd) {
   elems.add(anElemsToAdd);
}

And lastly you don't need to define new Integer[elems.size()] with the size defining it as elems.toArray(new Integer[0]) is sufficient

And after all the changes this is the final result

public static void main(String[] args) {
    TreeSet<Integer> elems = new TreeSet<>();
    int[] elemsToAdd = {1, 2, 3, 4};
    for (int anElemsToAdd : elemsToAdd) {
        elems.add(anElemsToAdd);
    }
    Integer[] elemsArray = elems.toArray(new Integer[0]);
}