Java IdentityHashMap put() Method

---

---

Description

The Java IdentityHashMap put(K key, V value) method is used to associate the specified value with the specified key in this identity hash map. If the map previously contained a mapping for this key, the old value is replaced.

Declaration

Following is the declaration for java.util.IdentityHashMap.put() method.

public V put(K key, V value)

Parameters

• key − This is the key with which the specified value is to be associated.

• value − This is the value to be associated with the specified key.

Return Value

The method call returns the previous value associated with key, or null if there was no mapping for key.

Exception

NA

Adding an Entry to an IdentityHashMap of Integer, Integer Pair 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 pairs. 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);
   }    
}

Output

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

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

Adding an Entry to an IdentityHashMap of Integer, String Pair 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,String. 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,String> newmap = new IdentityHashMap<>();

      // populate identity map
      newmap.put(1, "tutorials");
      newmap.put(2, "point");
      newmap.put(3, "is best"); 

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

Output

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

Map elements: {2=point, 3=is best, 1=tutorials}

Adding an Entry to an IdentityHashMap of Integer, Object Pair 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,Student pairs. 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,Student> newmap = new IdentityHashMap<>();

      // populate identity map
      newmap.put(1, new Student(1, "Julie"));
      newmap.put(2, new Student(2, "Robert"));
      newmap.put(3, new Student(3, "Adam"));

      System.out.println("Map elements: " + newmap);
   }    
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Output

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

Map elements: {1=[ 1, Julie ], 3=[ 3, Adam ], 2=[ 2, Robert ]}