Java.util.IdentityHashMap Class
Java IdentityHashMap Class
Java.util package provides an IdentityHashMap class which implements the Map interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values). In other words, in an IdentityHashMap, two keys k1 and k2 are considered equal if and only if (k1==k2). (In normal Map implementations (like HashMap) two keys k1 and k2 are considered equal if and only if (k1==null ? k2==null : k1.equals(k2)).)
This class provides all of the optional map operations, and permits null values and the null key. This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.
Class declaration
The declaration of java.util.IdentityHashMap class is:
public class IdentityHashMap<K,V>
extends AbstractMap<K,V>
implements Map<K,V>, Serializable, Cloneable
Here, K and V are the type of key and value respectively maintained by the container.
Class Constructors
| S.N | Constructors & Description |
|---|---|
| 1. |
IdentityHashMap() Constructs a new, empty identity hash map with a default expected maximum size (21). |
| 2. |
IdentityHashMap(int expectedMaxSize) Constructs a new, empty map with the specified expected maximum size. |
| 3. |
IdentityHashMap(Map<? extends K,? extends V> m) Constructs a new identity hash map containing the keys-value mappings in the specified map. |
java.util.IdentityHashMap Methods
The java.util.IdentityHashMap class has a number of methods which are listed below:
Member Methods
| S.N | Methods & Description |
|---|---|
| 1. |
void clear() Removes all of the mappings from this map. |
| 2. |
Object clone() Returns a shallow copy of this identity hash map: the keys and values themselves are not cloned. |
| 3. |
boolean containsKey(Object key) Tests whether the specified object reference is a key in this identity hash map. |
| 4. |
boolean containsValue(Object value) Tests whether the specified object reference is a value in this identity hash map. |
| 5. |
Set<Map.Entry<K,V>> entrySet() Returns a Set view of the mappings contained in this map. |
| 6. |
boolean equals(Object obj) Compares the specified object with this map for equality. |
| 7. |
void forEach(BiConsumer<? super K,? super V> action) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. |
| 8. |
V get(Object key) Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. |
| 9. |
int hashCode() Returns the hash code value for this map. |
| 10. |
boolean isEmpty() Returns true if this identity hash map contains no key-value mappings. |
| 11. |
Set<K> keySet() Returns an identity-based set view of the keys contained in this map. |
| 12. |
V put(K key, V value) Associates the specified value with the specified key in this identity hash map. |
| 13. |
void putAll(Map<? extends K,? extends V> m) Copies all of the mappings from the specified map to this map. |
| 14. |
V remove(Object key) Removes the mapping for this key from this map if present. |
| 15. |
void replaceAll(BiFunction<? super K,? super V,? extends V> function) Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception. |
| 16. |
int size() Returns the number of key-value mappings in this identity hash map. |
| 17. |
Collection<V> values() Returns a Collection view of the values contained in this map. |
Methods inherited
This class inherits the methods of following class:
- java.lang.Object
- java.util.AbstractMap<K,V>
