Introduction

The Java IdentityHashMap class implements the Map interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values).Following are the important points about IdentityHashMap −

• 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.

• In an IdentityHashMap, two keys k1 and k2 are considered equal if and only if (k1==k2), while in Map implementations (like HashMap) two keys k1 and k2 are considered equal if and only if (k1==null ? k2==null : k1.equals(k2)).

Class declaration

Following is the declaration for java.util.IdentityHashMap class −

public class IdentityHashMap<K,V>
   extends AbstractMap<K,V>
   implements Map<K,V>, Serializable, Cloneable

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.util.AbstractMap
• java.util.Object

Adding a Key-Value Mapping in an IdentityHashMap Example

The following example shows the usage of Java IdentityHashMap put() method to put few values in a Map. We”ve created a Map object of Integer,Integer. Then few entries are added using put() method and then map is printed.

package com.tutorialspoint;

import java.util.IdentityHashMap;

public class IdentityHashMapDemo {
   public static void main(String args[]) {
      
      // create identity map
      IdentityHashMap<Integer,Integer> newmap = new IdentityHashMap<>();

      // populate identity map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

      System.out.println("Map elements: " + newmap);
   }    
}

Let us compile and run the above program, this will produce the following result.

Map elements: {2=2, 3=3, 1=1}