What is a concurrent modification exception?
What is a concurrent modification exception?
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 you solve concurrent modification exception?
We can also avoid the Concurrent Modification Exception in a single threaded environment. We can use the remove() method of Iterator to remove the object from the underlying collection object. But in this case, you can remove only the same object and not any other object from the list.
Does HashMap throw ConcurrentModificationException?
You cannot remove an entry while looping over Map but you can remove a key or value while iterating over it. Since Iterator of HashMap is fail-fast it will throw ConcurrentModificationException if you try to remove entry using Map.
What causes Java Util ConcurrentModificationException?
Class ConcurrentModificationException. This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible. For example, it is not generally permissible for one thread to modify a Collection while another thread is iterating over it.
Which method of iterator throws concurrent modification exception?
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.
What iterator can throw a concurrent modification exception?
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.
Which method of the iterator throws concurrent modification exception?
How can we avoid ConcurrentModificationException in a multi threaded environment?
To Avoid ConcurrentModificationException in multi-threaded environment
- You can convert the list to an array and then iterate on the array.
- You can lock the list while iterating by putting it in a synchronized block.
- If you are using JDK1.
What is difference between Hashtable and ConcurrentHashMap?
Hashtable uses single lock for whole data. ConcurrentHashMap uses multiple locks on segment level (16 by default) instead of object level i.e. whole Map . ConcurrentHashMap locking is applied only for updates. So reads can happen very fast while writes are done with a lock.
How does the concurrent modification exception in Java work?
Java ConcurrentModificationException | How does It Work in Java? Java Programming Language provides a range of exception handling cases, and Concurrent Modification Exception is one of them.
What to do if ConcurrentModificationException is thrown?
You can use the iterator remove () function to remove the object from underlying collection object. But in this case, you can remove the same object and not any other object from the list. The output of the above program is shown below. You can see that there is no ConcurrentModificationException being thrown by the program.
Which is the child of ConcurrentModificationException in Java?
ConcurrentModificationException is the child class of RuntimeException and hence it is an unchecked exception.
Can a concurrent collection class be modified safely?
Concurrent Collection classes can be modified safely, they will not throw ConcurrentModificationException. In case of CopyOnWriteArrayList, iterator doesn’t accommodate the changes in the list and works on the original list. It is taking the new object added with key “4” but not the next added object with key “5”.