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WeakHashMap containsKey() Method in Java

Last Updated : 19 Jul, 2018
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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 
// Java code to illustrate the containsKey() 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);

        // 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));
    }
}
Output: 
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 
// Java code to illustrate the containsKey() method
import 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"));
    }
}
Output: 
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.

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