Java ConcurrentHashMap: entrySet() Example
February 09, 2022
entrySet() method of Java ConcurrentHashMap class. A ConcurrentHashMap is a hash table that supports full concurrency of retrievals and high expected concurrency for updates. The entrySet() is the method of ConcurrentHashMap with following Java doc.
Set<Map.Entry<K,V>> entrySet()
entrySet() method returns a Set view of map contained in this ConcurrentHashMap.
2. If this
ConcurrentHashMap changes, the Set view also changes and if this Set changes, the ConcurrentHashMap also changes.
3. If we remove the elements from this
Set, then the corresponding mapping is also removed from the map.
Using entrySet()
Here we will create aConcurrentHashMap and put some contents. Then we call entrySet() method on it. Using for loop, we iterate the set.
ConcurrentHashMap<String, Integer> conMap = new ConcurrentHashMap<>();
conMap.put("Mahesh", 22);
conMap.put("Nilesh", 25);
conMap.put("Krishn", 20);
conMap.put("Pradeep", 23);
Set<Entry<String, Integer>> entrySet = conMap.entrySet();
for (Map.Entry<String, Integer> mapEntry : entrySet) {
System.out.println(mapEntry.getKey() + " " + mapEntry.getValue());
}
Krishn 20 Mahesh 22 Pradeep 23 Nilesh 25
Remove Element
The element can be removed usingIterator.remove, Set.remove and Set.removeIf methods.
The changes in
Set view also perform the corresponding changes in ConcurrentHashMap.
Now find the ways to remove the elements.
1. Using
Iterator.remove
Iterator<Map.Entry<String, Integer>> iterator = conMap.entrySet().iterator();
while (iterator.hasNext()) {
Entry<String, Integer> entry = iterator.next();
if (entry.getValue() == 20) {
iterator.remove();
}
}
System.out.println(conMap);
{Mahesh=22, Pradeep=23, Nilesh=25}
Set.remove
Set<Entry<String, Integer>> entrySet = conMap.entrySet();
for (Map.Entry<String, Integer> mapEntry : entrySet) {
if (mapEntry.getKey().equals("Nilesh")) {
entrySet.remove(mapEntry);
}
}
System.out.println(conMap);
{Krishn=20, Mahesh=22, Pradeep=23}
Set.remove
Set<Entry<String, Integer>> entrySet = conMap.entrySet();
entrySet.removeIf(e -> e.getKey().equals("Krishn"));
System.out.println(conMap);
{Mahesh=22, Pradeep=23, Nilesh=25}
