Does list iterator throws concurrent modification exception?
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.
How do I fix concurrent modification exception in Java?
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.
How do I get rid of concurrent modification exception?
- How to Avoid ConcurrentModificationException in Java?
- CopyOnWriteArrayList in Java.
- Immutable List in Java.
- Custom ArrayList in Java.
- Difference Between Synchronized ArrayList and CopyOnWriteArrayList in Java Collection.
- AbstractQueue in Java with Examples.
- ArrayBlockingQueue Class in Java.
What happens if ArrayList is concurrently modified while iterating the elements?
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.
Is list iterator Fail Safe?
Answer: it doesn’t. The words “fail-safe” are never used in the Java SE specifications that describe the concurrent modification policy of a collection. As such, there is no reliable, consistent definition of “fail-safe” for an Iterator.
Is list iterator thread-safe?
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.
What is Iterator in Java?
An Iterator is an object that can be used to loop through collections, like ArrayList and HashSet. It is called an “iterator” because “iterating” is the technical term for looping. To use an Iterator, you must import it from the java. util package.
Is there a concurrent list in Java?
There is a concurrent list implementation in java.
Is Iterator Fail Safe?
Fail-Safe iterators don’t throw any exceptions if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection, not on the original collection and that’s why they are called fail-safe iterators.
Why do we get concurrent modification exception?
What Causes ConcurrentModificationException. The ConcurrentModificationException generally occurs when working with Java Collections. The Collection classes in Java are very fail-fast and if they are attempted to be modified while a thread is iterating over it, a ConcurrentModificationException is thrown.
How do you handle concurrent modification exception in ArrayList?
You can fix ConcurrentModificationException by changing your code and instead of using ArrayList. remove() method just use Iterator. remove() method in Java.
What happens when 2 threads try to modify an ArrayList?
There is no guaranteed behavior for what happens when add is called concurrently by two threads on ArrayList. However, it has been my experience that both objects have been added fine. Most of the thread safety issues related to lists deal with iteration while adding/removing.
Why ConcurrentHashMap is fail-safe?
This is because, they operate on the clone of the collection, not on the original collection and that’s why they are called fail-safe iterators. Iterator on CopyOnWriteArrayList, ConcurrentHashMap classes are examples of fail-safe Iterator.
Why iterator is fail-fast?
As name suggest fail-fast Iterators fail as soon as they realized that structure of Collection has been changed since iteration has begun. Structural changes means adding, removing or updating any element from collection while one thread is Iterating over that collection.
Is ConcurrentHashMap thread-safe?
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.
What is the difference between iterator and list iterator?
An Iterator is an interface in Java and we can traverse the elements of a list in a forward direction whereas a ListIterator is an interface that extends the Iterator interface and we can traverse the elements in both forward and backward directions.
How many types of iterators are there in Java?
three types
Iterators are used to traverse through the Java collections. There are three types of iterators.
Is ArrayList concurrent?
Implementation of ArrayList is not synchronized by default. It means if a thread modifies it structurally and multiple threads access it concurrently, it must be synchronized externally.
Why ArrayList is non synchronized?
ArrayList is non synchronized because if ArrayList is synchronized then only one thread can work on ArrayList at a time and rest of all threads cannot perform other operations on the ArrayList until the first thread release the lock. This causes overhead and reduces performance. This applies for all collections.
Why HashMap is fail-fast?
That aside, essentially, “fail-fast” in this sense means that an Iterator over a HashMap will throw an exception if it detects that another thread has modified the targeted HashMap – if you look in the source for HashMap, you will see this is done by simply checking a counter for the number of expected modifications.
How ConcurrentHashMap is fail-safe?
Iterator of ConcurrentHashMap is fail-safe, it means that it doesn’t throw ConcurrentModificationException even if underlying ConcurrentHashMap is modified once Iteration begins.
Can we modify Collection while iterating?
It is not generally permissible for one thread to modify a Collection while another thread is iterating over it. In general, the results of the iteration are undefined under these circumstances.
How do you avoid ConcurrentModificationException while iterating a HashMap?
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.
How does ConcurrentHashMap avoid 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. It may reflect the state when it was created and at some moment later.
What is difference between HashMap and ConcurrentHashMap?
HashMap is non-Synchronized in nature i.e. HashMap is not Thread-safe whereas ConcurrentHashMap is Thread-safe in nature. HashMap performance is relatively high because it is non-synchronized in nature and any number of threads can perform simultaneously.