Java Remove Specific Item From ConcurrentHashMap
The remove
method does synchronize on a lock. Indeed checking the code of ConcurrentHashMap#remove()
, there is a call to a lock
method that acquires the lock:
public V remove(Object key) {
int hash = hash(key.hashCode());
return segmentFor(hash).remove(key, hash, null);
}
where ConcurrentHashMap.Segment#remove(key, hash, null)
is defined as:
V remove(Object key, int hash, Object value) {
lock();
try {
...
Note the Javadoc description:
Retrieval operations (including
get
) generally do not block, so may overlap with update operations (includingput
andremove
). Retrievals reflect the results of the most recently completed update operations holding upon their onset. For aggregate operations such asputAll
andclear
, concurrent retrievals may reflect insertion or removal of only some entries. Similarly, Iterators and Enumerations return elements reflecting the state of the hash table at some point at or since the creation of the iterator/enumeration. They do not throwConcurrentModificationException
. However, iterators are designed to be used by only one thread at a time.
An Iterator should do the job:
Iterator<Map.Entry<String, Integer>> iterator = storage.entrySet().iterator();
while(iterator.hasNext())
{
Map.Entry<String, Integer> entry = iterator.next();
if(entry.getKey().equals("First"))
{
iterator.remove();
}
}
Reference: https://dzone.com/articles/removing-entries-hashmap