Change the ArrayList into TreeSet.

Sure, here's an example of how to change an ArrayList into a TreeSet:

import java.util.ArrayList;
import java.util.TreeSet;

public class Example {
    public static void main(String[] args) {
        ArrayList<Integer> arrayList = new ArrayList<>();
        arrayList.add(5);
        arrayList.add(2);
        arrayList.add(8);
        arrayList.add(1);
        arrayList.add(9);

        // Convert the ArrayList to a TreeSet
        TreeSet<Integer> treeSet = new TreeSet<>(arrayList);

        // Print the TreeSet
        System.out.println(treeSet);
    }
}

In this example, we first create an ArrayList of integers. We then create a TreeSet and pass the ArrayList to its constructor. This automatically creates a sorted set with the elements of the ArrayList. Finally, we print the TreeSet to verify that it is sorted.