Which of the following correctly describes the behavior of the following code? List list = new ArrayList<>(); list.add("A"); list.add("B"); for (String s : list) { if (s.equals("A")) { list.remove(s); } } System.out.println(list);

Working with Arrays and Collections →hardMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

Which of the following correctly describes the behavior of the following code? List<String> list = new ArrayList<>(); list.add("A"); list.add("B");

for (String s : list) {
    if (s.equals("A")) {

list.remove(s);

}
}

System.out.println(list);

⚠ Common exam trap

A common mix-up: candidates think the for-each loop will safely remove the element and continue, or that the exception only occurs with multiple threads, but in fact any structural modification (add, remove, clear) to the underlying collection during single-threaded iteration triggers the fail-fast mechanism.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

ConcurrentModificationException is thrown

The code uses an enhanced for-each loop to iterate over an ArrayList while calling `list.remove(s)` when the element equals "A". This modifies the list structurally during iteration, which causes the iterator (used internally by the for-each loop) to detect the concurrent modification and throw a `ConcurrentModificationException` at runtime. The exception is thrown because the iterator's `modCount` check fails when the list is modified outside of the iterator's own `remove` method.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
ConcurrentModificationException is thrown
Why this is correct
Fail-fast behavior.
✗
Compilation error
Why it's wrong here
Code compiles correctly.
✗
[B]
Why it's wrong here
Exception thrown before completing iteration.
✗
[A, B] unchanged
Why it's wrong here
Modification causes exception.

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1Z0-829 Working with Arrays and Collections Practice Question

Why each option matters

Option-by-option breakdown

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