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Showing content from https://www.geeksforgeeks.org/java/identityhashmap-putall-method-in-java/ below:

IdentityHashMap putAll() Method in Java

Last Updated : 24 Jul, 2018

The java.util.IdentityHashMap.putAll() is an inbuilt method of IdentityHashMap class that is used for the copy operation. The method copies all of the elements i.e., the mappings, from one map into another.

Syntax:

new_Identityhash_map.putAll(exist_Identityhash_map)

Parameters:

The method takes one parameter

exist_Identityhash_map

that refers to the existing map we want to copy from.

Return Value:

The method does not return any values.

Exception:

The method throws

NullPointerException

if the map we want to copy from is NULL. Below programs illustrates the working of java.util.IdentityHashMap.putAll() method:

Program 1:

Mapping String Values to Integer Keys.

Java


 // Java code to illustrate the putAll() method
import java.util.*;

public class Identity_Hash_Map_Demo {
    public static void main(String[] args)
    {

        // Creating an empty IdentityHashMap
        Map<Integer, String> Identity_hash = new 
                      IdentityHashMap<Integer, String>();

        // Mapping string values to int keys
        Identity_hash.put(10, "Geeks");
        Identity_hash.put(15, "4");
        Identity_hash.put(20, "Geeks");
        Identity_hash.put(25, "Welcomes");
        Identity_hash.put(30, "You");

        // Displaying the IdentityHashMap
        System.out.println("Initial Mappings are: " + 
                                           Identity_hash);

        // Creating a new Identityhash map and copying
        Map<Integer, String> new_Identityhash_map = new 
                        IdentityHashMap<Integer, String>();
        new_Identityhash_map.putAll(Identity_hash);

        // Displaying the final IdentityHashMap
        System.out.println("The new map: " + 
                                    new_Identityhash_map);
    }
}

Output:

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
The new map: {15=4, 30=You, 10=Geeks, 25=Welcomes, 20=Geeks}

Program 2:

Mapping Integer Values to String Keys.

Java


 // Java code to illustrate the putAll() method
import java.util.*;

public class IdentityHash_Map_Demo {
    public static void main(String[] args)
    {

        // Creating an empty IdentityHashMap
        Map<String, Integer> Identity_hash = new 
                      IdentityHashMap<String, Integer>();

        // Mapping int values to string keys
        Identity_hash.put("Geeks", 10);
        Identity_hash.put("4", 15);
        Identity_hash.put("Geeks", 20);
        Identity_hash.put("Welcomes", 25);
        Identity_hash.put("You", 30);

        // Displaying the IdentityHashMap
        System.out.println("Initial Mappings are: " + 
                                          Identity_hash);

        // Creating a new Identityhash map and copying
        Map<String, Integer> new_Identityhash_map = new 
                      IdentityHashMap<String, Integer>();
        new_Identityhash_map.putAll(Identity_hash);

        // Displaying the final IdentityHashMap
        System.out.println("The new map: " + 
                                   new_Identityhash_map);
    }
}

Output:

Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
The new map: {Welcomes=25, 4=15, You=30, Geeks=20}

Note:

The same operation can be performed with any type of Mappings with variation and combination of different data types.

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