Challenge 2: ConcurrentModificationException and the Iterator Fix — Possible Solution
====================================================================

Broken attempt — RemoveDemo.java:

import java.util.ArrayList;
import java.util.List;

public class RemoveDemo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>(List.of("Alice", "Bob", "Carol", "Bob"));

        for (String name : names) {
            if (name.equals("Bob")) {
                names.remove(name);   // removing directly on the list mid-for-each
            }
        }
    }
}

Representative runtime exception:

    Exception in thread "main" java.util.ConcurrentModificationException
        at java.base/java.util.ArrayList$Itr.checkForComodification(...)
        at java.base/java.util.ArrayList$Itr.next(...)
        at RemoveDemo.main(RemoveDemo.java:8)

Fixed — RemoveDemo.java:

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class RemoveDemo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>(List.of("Alice", "Bob", "Carol", "Bob"));

        Iterator<String> it = names.iterator();
        while (it.hasNext()) {
            String name = it.next();
            if (name.equals("Bob")) {
                it.remove();   // safe -- the iterator itself performs the removal
            }
        }

        System.out.println(names);
    }
}

Output:

    [Alice, Carol]

Explanation:
The for-each loop uses a hidden Iterator internally. Calling
names.remove(...) directly changes the list's structure without that
hidden iterator knowing, so its next call to next() detects the
mismatch and throws. Using the Iterator's own remove() keeps the
iterator's internal state in sync with the list, since the iterator
itself is the one performing the removal.

WHY THIS WORKS AS AN ANSWER
------------------------------
This reproduces the exact ConcurrentModificationException the
chapter's warn-box describes, then applies the chapter's own stated
fix -- Iterator.remove() -- as the only safe way to remove elements
during iteration.