WeakHashMap put() Method in Java

The java.util.WeakHashMap.put() method of WeakHashMap is used to insert a mapping into a map. This means we can insert a specific key and the value it is mapping, into a particular map. If an existing key is passed then the previous value gets replaced by the new value. If a new pair is passed, then the pair gets inserted as a whole.

Syntax:

Weak_Hash_Map.put(key, value)

Parameters: The method takes two parameters, both are of the Object type of the WeakHashMap.



  • key: This refers to the key element that needs to be inserted into the Map for mapping.
  • value: This refers to the value that the above key would map into.

Return Value: If an existing key is passed then the previous value gets returned. If a new pair is passed, then NULL is returned.

Below programs are used to illustrate the working of java.util.WeakHashMap.put() Method:
Program 1: When passing an existing key.

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java code to illustrate the put() method
import java.util.*;
  
public class Weak_Hash_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty WeakHashMap
        Map<Integer, String> weak_hash = new 
                  WeakHashMap<Integer, String>();
  
        // Mapping string values to int keys
        weak_hash.put(10, "Geeks");
        weak_hash.put(15, "4");
        weak_hash.put(20, "Geeks");
        weak_hash.put(25, "Welcomes");
        weak_hash.put(30, "You");
  
        // Displaying the WeakHashMap
        System.out.println("Initial Mappings are: " + 
                                           weak_hash);
  
        // Inserting existing key along with new value
        String returned_value = 
                     (String)weak_hash.put(20, "All");
  
        // Verifying the returned value
        System.out.println("Returned value is: " + 
                                   returned_value);
  
        // Displayin the new map
        System.out.println("New map is: " + weak_hash);
    }
}

chevron_right






                        filter_none









Output:


Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
Returned value is: Geeks
New map is: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=All}





Program 2: When passing a new key.











                                    filter_none




                                    edit

                                    close




                                    play_arrow




                                    link

                                    brightness_4

                                    code
                                




















// Java code to illustrate the put() method 


import java.util.*; 


  


public class Weak_Hash_Map_Demo { 


    public static void main(String[] args) 


    { 


  


        // Creating an empty WeakHashMap 


        Map<Integer, String> weak_hash = new 


                 WeakHashMap<Integer, String>(); 


  


        // Mapping string values to int keys 


        weak_hash.put(10, "Geeks"); 


        weak_hash.put(15, "4"); 


        weak_hash.put(20, "Geeks"); 


        weak_hash.put(25, "Welcomes"); 


        weak_hash.put(30, "You"); 


  


        // Displaying the WeakHashMap 


        System.out.println("Initial Mappings are: " +  


                                          weak_hash); 


  


        // Inserting existing key along with new value 


        String returned_value =  


                      (String)weak_hash.put(50, "All"); 


  


        // Verifying the returned value 


        System.out.println("Returned value is: " +  


                                      returned_value); 


  


        // Displayin the new map 


        System.out.println("New map is: " + weak_hash); 


    } 


} 



















                        chevron_right







                        filter_none









Output:


Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
Returned value is: null
New map is: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks, 50=All}





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



          
          
          
          

            

    

        My Personal Notes
        arrow_drop_up
    

    

        
        

            
            
        

    


Recommended Posts:
Chinmoy Lenka
Check out this Author's contributed articles.
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on  the "Improve Article" button below.