Sorry I can't figure this out >.<

Hello Tian, Like Kaiyr said, you cannot use a regular for loop to manipulate a set. This where Iterator comes into play. You might of also tried to use the for each loop to remove from a set and got an Exception in thread "main" java.util.ConcurrentModificationException This is because you cannot go through a Collection and modify it at the same time with a for each loop. Hint: Use Iterator. The Iterator class have three functions/methods that will be of use to you: 1. iterator.hasNext() 2. iterator.next() 3. iterator.remove() You can declare and initialize an Iterator like this:

Iterator<Data-Type> iterator = collectionYouWantToIterate.iterator()

// Data-Type = The data type the data structure is holding (e.g Integer).
// collectionYouWantToIterate = The name you have is set.

More information on how to use Iterator: https://www.geeksforgeeks.org/how-to-use-iterator-in-java/ Note: On line 24 of your code, where you have set.contains(j>10). This is comparing the current j to see if it is greater than 10 and then put the result (boolean value) into the contains method.

Hi there. Regular loops do not work with sets. to iterate thru set use for each loop: for(Integer i:set) { if i>10.....then remove the object from the set. Hint. Use the remove() method of a set object.