Java IdentityHashMap putAll() Method

---

---

Description

The Java IdentityHashMap putAll(Map<? extends K,? extends V> t) method is used to copy all of the mappings from the specified map to this map.

Declaration

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

public void putAll(Map<? extends K,? extends V> t)

Parameters

t − This is the mappings to be stored in this map.

Return Value

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

Exception

NullPointerException − This is thrown if the specified map is null.

Adding Multiple entries to an IdentityHashMap of Integer, Integer Pair Example

The following example shows the usage of Java IdentityHashMap putAll() 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. A new map is populated using putAll() method and then 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<>();
	  IdentityHashMap<Integer,Integer> newmap2 = new IdentityHashMap<>();
 
      // populate identity map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

      System.out.println("Map elements: " + newmap);
      newmap2.putAll(newmap);
      System.out.println("Map elements: " + newmap2); 
   }    
}

Output

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

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

Adding Multiple entries to an IdentityHashMap of Integer, String Pair Example

The following example shows the usage of Java IdentityHashMap putAll() method to put few values in a Map. We've created a Map object of Integer,String pairs. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then 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<>();
	  IdentityHashMap<Integer,String> newmap2 = new IdentityHashMap<>();
      // populate identity map
      newmap.put(1, "tutorials");
      newmap.put(2, "point");
      newmap.put(3, "is best"); 

      System.out.println("Map elements: " + newmap);
      newmap2.putAll(newmap);
      System.out.println("Map elements: " + newmap2);
   }    
}

Output

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

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

Adding Multiple entries to an IdentityHashMap of Integer, Object Pair Example

The following example shows the usage of Java IdentityHashMap putAll() 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. A new map is populated using putAll() method and then 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<>();
      IdentityHashMap<Integer,Student> newmap2 = 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);
      newmap2.putAll(newmap);
      System.out.println("Map elements: " + newmap2);
   }    
}
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 ]}
Map elements: {1=[ 1, Julie ], 3=[ 3, Adam ], 2=[ 2, Robert ]}