Synchronize forEach() in SynchronizedCollection

[rootvector2]

noticed while diffing the overridden method list against java.util.Collections.synchronizedCollection: SynchronizedCollection guards removeIf but never overrides forEach, so the inherited default walks the deliberately unsynchronized iterator() and a concurrent writer trips ConcurrentModificationException; delegating forEach under lock covers SynchronizedBag, SynchronizedSortedBag, SynchronizedMultiSet, SynchronizedSortedMultiSet and SynchronizedQueue too since they all extend it, while stream() and spliterator() stay unsynchronized for the same reason the JDK leaves them so: their traversal happens after the lock would be released.

• Read the contribution guidelines for this project.
• Read the ASF Generative Tooling Guidance if you use Artificial Intelligence (AI).
• I used AI to create any part of, or all of, this pull request. Which AI tool was used to create this pull request, and to what extent did it contribute?
• Run a successful build using the default Maven goal with mvn; that's mvn on the command line by itself.
• Write unit tests that match behavioral changes, where the tests fail if the changes to the runtime are not applied. This may not always be possible, but it is a best practice.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Each commit in the pull request should have a meaningful subject line and body.

[Copilot]

Pull request overview

This PR aligns org.apache.commons.collections4.collection.SynchronizedCollection with java.util.Collections.synchronizedCollection by synchronizing forEach(...) on the decorator’s lock, preventing traversal via the deliberately-unsynchronized iterator() default implementation.

Changes:

• Override SynchronizedCollection#forEach(Consumer) to delegate under synchronized (lock).
• Add a parameterized JUnit 5 test that asserts forEach executes while holding the decorator monitor across all affected synchronized decorators.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/main/java/org/apache/commons/collections4/collection/SynchronizedCollection.java	Adds a forEach override synchronized on lock to avoid unsynchronized iteration.
src/test/java/org/apache/commons/collections4/collection/SynchronizedCollectionTest.java	Adds parameterized coverage ensuring forEach holds the expected lock for multiple synchronized decorators.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[garydgregory]

Thank you @rootvector2 , merged 🚀