```java import java.util.ArrayList; import java.util.List; public class StreamTest { public static void main(String[] args) { List<String> names = new ArrayList<>(); names.add("Ivan"); names.add("Max"); names.add("Alex"); names.stream().forEach(name -> { System.out.println(name); names.add(name + " the Great"); }); System.out.println(names); } } ```

In this code, the list names is modified during iteration through it using the Stream API.

Java Stream does not support modifying the collection while processing it — this will lead to a ConcurrentModificationException.

In your example:

names.stream().forEach(name -> {
    System.out.println(name);
    names.add(name + " the Great");
});

Attempting to add elements to names during traversal will throw an exception.

If you run this code, you will get:

Exception in thread "main" java.util.ConcurrentModificationException
    at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043)
    at java.base/java.util.ArrayList$Itr.next(ArrayList.java:997)
    at ...

To avoid the error, do not modify the collection during iteration. For example, collect new elements in a separate list, then add them:

List<String> additions = new ArrayList<>();
names.stream().forEach(name -> {
    System.out.println(name);
    additions.add(name + " the Great");
});
names.addAll(additions);
System.out.println(names);

This way, you safely extend the list after the iteration.