Does HashMap give ConcurrentModificationException?
Does HashMap give ConcurrentModificationException?
Since Iterator of HashMap is fail-fast it will throw ConcurrentModificationException if you try to remove entry using Map.
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.
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.
Does Iterator throw a ConcurrentModificationException?
ConcurrentModificationException is not thrown by Iterator. remove() because that is the permitted way to modify an collection while iterating. This is what the javadoc for Iterator says: Removes from the underlying collection the last element returned by this iterator (optional operation).
How do I get around ConcurrentModificationException?
To Avoid ConcurrentModificationException in multi-threaded environment. You can convert the list to an array and then iterate on the array. This approach works well for small or medium size list but if the list is large then it will affect the performance a lot.
Does iterator throw a ConcurrentModificationException?
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.
What iterator can throw a ConcurrentModificationException Mcq?
The Fail Fast iterator throws a ConcurrentModificationException if a collection is modified while iterating over it. The Fail Fast iterator uses an original collection to traverse over the collection’s elements.
Can we remove an element by using for each loop?
The program needs access to the iterator in order to remove the current element. The for-each loop hides the iterator, so you cannot call remove .
What can a for-each loop do?
It is mainly used to traverse the array or collection elements. The advantage of the for-each loop is that it eliminates the possibility of bugs and makes the code more readable. It is known as the for-each loop because it traverses each element one by one.
Can you use a forEach loop on an ArrayList?
As of Java 8, we can use the forEach method as well as the iterator class to loop over an ArrayList.
When do you get ConcurrentModificationException in Java?
…without any modification exception. You will probably want to synchronize this in case something else is also looking at / mucking with that entry. Iterating over a Map and adding entries at the same time will result in a ConcurrentModificationException for most Map classes.
How to avoid ConcurrentModificationException when iterating over a map?
This doesn’t work well, since you shouldn’t be modifying a map whilst your iterating through it (method is synchronised, but ConcurrentModificationException still appears) My question is, if I need to iterate over a map and change values, what are the best practices/methods I can use for doing so?
When does iterator throw exception in Java concurrent modification?
For example, if a thread modifies a collection directly while it is iterating over the collection with a fail-fast iterator, the iterator will throw this exception. In your case, you have modified the collection after creating the iterator and hence you have encountered the exception.