Does map throw ConcurrentModificationException?

Since Iterator of HashMap is fail-fast it will throw ConcurrentModificationException if you try to remove entry using Map. remove(Object key) method, the right way to remove an entry from the HashMap by using Iterator’s remove() method.

How do you prevent ConcurrentModificationException on a map?

use ConcurrentHashMap. keep on using simple HashMap, but build a new map on each modification and switch maps behind the scenes (synchronizing the switch operation or using AtomicReference)

How do you resolve ConcurrentModificationException?

How to avoid ConcurrentModificationException in a multi-threaded environment?

1. Instead of iterating over the collection class, we can iterate over the array.
2. Another way can be locking the list by putting it in the synchronized block.
3. JDK 1.5 or higher provides with ConcurrentHashMap and CopyOnWriteArrayList classes.

How can you avoid ConcurrentModificationException while iterating a collection?

How to avoid ConcurrentModificationException in a multi-threaded environment?

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

Is TreeMap concurrent?

Both TreeMap and TreeSet are safe when read, even concurrently, by multiple threads. So if they have been created and populated by a single thread (say, at the start of the program), and only then read, but not modified by multiple threads, there’s no reason for synchronization or locking.

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 is fail-fast in iterator?

Fail-fast iterators checks the modCount flag whenever it gets the next value (i.e. using next() method), and if it finds that the modCount has been modified after this iterator has been created, it throws ConcurrentModificationException.

Is TreeMap thread-safe in Java?

TreeMap and TreeSet are not thread-safe collections, so care must be taken to ensure when used in multi-threaded programs. Both TreeMap and TreeSet are safe when read, even concurrently, by multiple threads.

What is difference between HashMap and TreeMap?

HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap allows homogeneous values as a key because of sorting.

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?

Where is ConcurrentModificationException thrown in abstractlist class?

One thing is that the checkForComodification() method is present in add() and remove() methods of AbstractList class and that throws ConcurrentModificationException whenever we try to add or remove items. In the article it is mentioned that it is thrown from next() method.

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.