The java.util.WeakHashMap.keySet() method in Java is used to create a set out of the key elements contained in the hash map. It basically returns a set view of the keys or we can create a new set and store the key elements in them.
Syntax:
Weak_Hash_Map.keySet()
Parameters: The method does not take any parameter.
Return Value: The method returns a set having the keys of the weak hash map.
Below programs are used to illustrate the working of java.util.WeakHashMap.keySet() Method:
Program 1: Mapping String Values to Integer Keys.
// Java code to illustrate the keySet() 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);          // Using keySet() to get the set view of keys        System.out.println("The set is: " +                                   weak_hash.keySet());    }} |
Output:
Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
The set is: [30, 15, 10, 25, 20]
Program 2: Mapping Integer Values to String Keys.
// Java code to illustrate the keySet() methodimport java.util.*;  public class Weak_Hash_Map_Demo {    public static void main(String[] args)    {          // Creating an empty WeakHashMap        Map<String, Integer> weak_hash =                     new WeakHashMap<String, Integer>();          // Mapping int values to string keys        weak_hash.put("Geeks", 10);        weak_hash.put("4", 15);        weak_hash.put("Geeks", 20);        weak_hash.put("Welcomes", 25);        weak_hash.put("You", 30);          // Displaying the WeakHashMap        System.out.println("Initial Mappings are: " +                                            weak_hash);          // Using keySet() to get the set view of keys        System.out.println("The set is: " +                                   weak_hash.keySet());    }} |
Output:
Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
The set is: [Welcomes, 4, You, Geeks]
Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.
