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What is Java 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 stop ConcurrentModificationException in Java?
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.
Which method 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 does ConcurrentHashMap works in Java?
ConcurrentHashMap class is thread-safe i.e. multiple threads can operate on a single object without any complications. At a time any number of threads are applicable for a read operation without locking the ConcurrentHashMap object which is not there in HashMap. The default concurrency-level of ConcurrentHashMap is 16.
What is fail first in Java?
Fail Fast Iterator. The iterator in Java is used to traverse over a collection’s objects. The collections return two types of iterators, either it will be Fail Fast or Fail Safe. The Fail Fast iterators immediately throw ConcurrentModificationException in case of structural modification of the collection.
Is iterator thread-safe in Java?
No iterator is thread-safe. If the underlying collection is changed amidst iteration, a ConcurrentModificationException is thrown. Even iterators of synchronized collections are not thread-safe – you have to synchronize manually. One exception is the CopyOnWriteArrayList , which holds a snapshot during iteration.
When does ConcurrentModificationException happen in Java-javatpoint?
It can also happen if a single thread has some methods called which are trying to violate the contract of the object. This may happen when a thread is trying to modify the Collection object while it is being iterated by some fail-fast iterator, the iterator will throw the exception.
When is an exception thrown for concurrent modification?
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.
How to create a concurrent modification in Java?
Between creating the iterator and starting to use the iterator, you added arguments to the list that is to be iterated. This is a concurrent modification. ListIterator it = s.listIterator (); for (String a : args) s.add (a); // concurrent modification here if (it.hasNext ()) String item = it.next (); // exception thrown here
How to avoid ConcurrentModificationException in multi-threaded environment?
To avoid the ConcurrentModificationException in a multi-threaded environment, we can follow the following ways- Instead of iterating over the collection class, we can iterate over the array. In this way, we can work very well with small-sized lists, but this will deplete the performance if the array size is very large.