The java.util.WeakHashMap.containsKey() method is used to check whether a particular key is being mapped into the WeakHashMap or not. It takes the key element as a parameter and returns True if that element is mapped in the map.
Syntax:
Weak_Hash_Map.containsKey(key_element)
Parameters: The method takes just one parameter key_element that refers to the key whose mapping is supposed to be checked inside a map.
Return Value: The method returns boolean true if the presence of the key is detected else false .
Below programs are used to illustrate the working of java.util.WeakHashMap.containsKey() Method:
Program 1: Mapping String Values to Integer Keys.
// Java code to illustrate the containsKey() 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);          // Checking for the key_element '20'        System.out.println("Is the key '20' present? " +                                   weak_hash.containsKey(20));          // Checking for the key_element '5'        System.out.println("Is the key '5' present? " +                                    weak_hash.containsKey(5));    }} |
Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
Is the key '20' present? true
Is the key '5' present? false
Program 2: Mapping Integer Values to String Keys.
// Java code to illustrate the containsKey() 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);          // Checking for the key_element 'Welcomes'        System.out.println("Is the key 'Welcomes' present? " +                                   weak_hash.containsKey("Welcomes"));          // Checking for the key_element 'World'        System.out.println("Is the key 'World' present? " +                                       weak_hash.containsKey("World"));    }} |
Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
Is the key 'Welcomes' present? true
Is the key 'World' present? false
Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.
