What causes ConcurrentModificationException?

The ConcurrentModificationException occurs when an object is tried to be modified concurrently when it is not permissible. This exception usually comes when one is working with Java Collection classes. For Example – It is not permissible for a thread to modify a Collection when some other thread is iterating over it.

How do I fix ConcurrentModificationException?

How do you fix Java’s ConcurrentModificationException? There are two basic approaches: Do not make any changes to a collection while an Iterator loops through it. If you can’t stop the underlying collection from being modified during iteration, create a clone of the target data structure and iterate through the clone.

What is difference between forEach and iterator?

Difference between the two traversals In for-each loop, we can’t modify collection, it will throw a ConcurrentModificationException on the other hand with iterator we can modify collection. Modifying a collection simply means removing an element or changing content of an item stored in the collection.

Does iterator throw a ConcurrentModificationException?

ConcurrentModificationException is not thrown by Iterator. remove() because that is the permitted way to modify an collection while iterating.

How do I stop ConcurrentModificationException?

How to avoid ConcurrentModificationException in a multi-threaded environment?

We can iterate over the array instead of iterating over the collection class.
Locking the list by putting it in the synchronized block is another way to avoid the concurrent modification exception.

Can ConcurrentHashMap throws ConcurrentModificationException?

ConcurrentHashMap does not throw ConcurrentModificationException if the underlying collection is modified during an iteration is in progress. Iterators may not reflect the exact state of the collection if it is being modified concurrently.

How do you overcome ConcurrentModificationException in Java?

What is forEachRemaining in Java?

The forEachRemaining() method of Java Interface Spliterator is used to performs the given action for each remaining element sequentially in the current thread until all elements have been processed or the action throws an exception.

Which method of iterator throws ConcurrentModificationException?

If we invoke a sequence of methods on an object that violates its contract, then the object throws ConcurrentModificationException. For example: if while iterating over the collection, we directly try to modify that collection, then the given fail-fast iterator will throw this ConcurrentModificationException.

How many ways we can avoid ConcurrentModificationException?

Methods: Here two ways are proposed of which starting with the naive one and ending up with the optimal approach to reach the goal. Using Loops: We used the Iterator remove() method instead of that we can use a for loop to avoid ConcurrentModificationException in a Single-threaded environment.