Adding a new item to the tree also adds it to a partial copy of the tree.

Question

In the following code, we create two different TreeSet objects.

We assign some values ​​to the first object, and then assign a subset of the 1st object to the second object. Then we add the element (609) to the 1st object only . Why then does this new element appear in both objects?

import java.util.*;
public class Explorer1 {
    public static void main(String[] args) {
        TreeSet<Integer> s = new TreeSet<Integer>();
        TreeSet<Integer> subs = new TreeSet<Integer>();
        for(int i = 606; i < 613; i++)
            if(i%2 == 0) s.add(i);
        subs = (TreeSet)s.subSet(608, true, 611, true);
        s.add(609);
        System.out.println(s + " " + subs);
    }
}

Output: [606, 608, 609, 610, 612] [608, 609, 610]

Answer 1

The answer is in the documentation :

, , . , .

, , , :

subs = new TreeSet<>(s.subSet(608, true, 611, true));

, . TreeSet, TreeSet<Integer>:

subs = (TreeSet<Integer>)s.subSet(608, true, 611, true);