Trying to cast setInstance.toArray() to Integer[], no compile time error but there is run time error, why?

Question

I'm experimenting with Java HashSet class and its toArray() method. Below is the code I have came up with. The compiler did not display any error but when I run the code, the IDE outputs the error message:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Integer;
    at JTOCollection.TheCollectionInterface.main(TheCollectionInterface.java:26)
Java Result: 1

Due to my inexperience, I can't fully understand the complete reason behind the error message, could someone please explain it to me?

Set<Integer> set1 = new HashSet<>();
set1.add(1);
set1.add(2);
set1.add(3);
set1.add(2);

Integer[] intArray = (Integer[]) set1.toArray();
for(Integer i : intArray){
    System.out.println(i);
}

Answer 1

because you are using public Object[] toArray() instead of public <T> T[] toArray(T[] a).

use this:

Integer[] intArray =  set1.toArray(new Integer[set1.size()]);

docs for : public <T> T[] toArray(T[] a)

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.