Regarding the answe

public static HashSet<Integer> removeAllNumbersGreaterThan10(HashSet<Integer> set) { // write your code here for(Integer n : set){ if(n > 10){ set.remove(n); } } return set;} I apologize, but I forgot to copy my code. This is my original code, and the last requirement didn't pass.

Do not write code blindly, always test it. For that you can use the main method. I admit I did not do here either ;) but I'm sure your code will throw a ConcurrentModificationException and that will prohibit it from validating. Reason: When using an Iterator to walk over a collection you may only use the Iterators functionality to modify that collection. A for-each loop internally uses an Iterator but you used the collections methods to modify it (set.remove()) -> ConcurrentModificationException Possible test code:

public static void main(String[] args) {
    Set<Integer> set = createSet();
    removeAllNumbersGreaterThan10(set);
    set.forEach(System.out::println);
}

Thank you, I understand now.