ConcurrentHashMap

Creates a new, empty map with the specified initial capacity and the specified load factor.

Creates a new, empty map with the specified initial capacity, and with default load factor and concurrencyLevel.

Creates a new, empty map with a default initial capacity, load factor, and concurrencyLevel.

Creates a new map with the same mappings as the given map. The map is created with a capacity of twice the number of mappings in the given map or 11 (whichever is greater), and a default load factor.

Removes all mappings from this map.

Legacy method testing if some key maps into the specified value in this table. This method is identical in functionality to containsValue(Object), and exists solely to ensure full compatibility with class Hashtable, which supported this method prior to introduction of the Java Collections framework.

Tests if the specified object is a key in this table.

Returns true if this map maps one or more keys to the specified value. Note: This method requires a full internal traversal of the hash table, and so is much slower than method containsKey.

Returns an enumeration of the values in this table.

Returns a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations. The returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Returns the value to which the specified key is mapped in this table.

Returns whether this map is empty.

Returns a set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations. The returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Returns an enumeration of the keys in this table.

Maps the specified key to the specified value in this table. Neither the key nor the value can be null.

The value can be retrieved by calling the get method with a key that is equal to the original key.

Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified Map.

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

   if (!map.containsKey(key)) 
      return map.put(key, value);
   else
      return map.get(key);
 

Remove entry for key only if currently mapped to given value. Acts as

 
  if (map.get(key).equals(value)) {
     map.remove(key);
     return true;
 } else return false;
 

Removes the key (and its corresponding value) from this table. This method does nothing if the key is not in the table.

Replace entry for key only if currently mapped to given value. Acts as

 
  if (map.get(key).equals(oldValue)) {
     map.put(key, newValue);
     return true;
 } else return false;
 

Replace entry for key only if currently mapped to some value. Acts as

 
  if ((map.containsKey(key)) {
     return map.put(key, value);
 } else return null;
 

Returns the number of elements in this map.

Returns a collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations. The returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.