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.
// Java code to illustrate the put() methodimport 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);    }} |
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.
// Java code to illustrate the put() methodimport 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);    }} |
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.
