Hashtable contains() Method in Java

The java.util.Hashtable.contains(Object value) method in Java is used to check whether a particular value is being mapped by any keys present in the Hashtable. 

Syntax:

Hash_table.contains(Object value)

Parameters: The method accepts one parameter value of object type and refers to the value of the hashtable whose mapping is to be verified. 

Return Value: The method returns a boolean true value if the passed value is mapped by any of the keys in the Hashtable. Exceptions: The method throws NullPointerException if the passed value is Null. 

Below programs illustrate the working of the above-mentioned method: 

Program 1:

Java

// Java code to illustrate the contains() method
import java.util.*;

public class Hash_Table_Demo {
    public static void main(String[] args)
    {

        // Creating an empty Hashtable
        Hashtable<Integer, String> hash_table =
        new Hashtable<Integer, String>();

        // Mapping string values to int keys
        hash_table.put(10, "Geeks");
        hash_table.put(15, "4");
        hash_table.put(20, "Geeks");
        hash_table.put(25, "Welcomes");
        hash_table.put(30, "You");

        // Displaying the HashMap
        System.out.println("Initial Table is: " + hash_table);

        // Checking for the Value 'Geeks'
        System.out.println("Is the value 'Geeks' present? " +
        hash_table.contains("Geeks"));

        // Checking for the Value 'World'
        System.out.println("Is the value 'World' present? " +
        hash_table.contains("World"));
    }
}

Output:

Initial Table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Is the value 'Geeks' present? true
Is the value 'World' present? false

Program 2:

Java

// Java code to illustrate the contains() method
import java.util.*;

public class Hash_Table_Demo {
    public static void main(String[] args)
    {

        // Creating an empty Hashtable
        Hashtable<String, Integer> hash_table =
        new Hashtable<String, Integer>();

        // Mapping int values to string keys
        hash_table.put("Geeks", 10);
        hash_table.put("4", 15);
        hash_table.put("Geeks", 20);
        hash_table.put("Welcomes", 25);
        hash_table.put("You", 30);

        // Displaying the Hashtable
        System.out.println("Initial Mappings are: " + hash_table);

        // Checking for the Value '10'
        System.out.println("Is the value '10' present? " +
        hash_table.containsValue(10));

        // Checking for the Value '30'
        System.out.println("Is the value '30' present? " +
        hash_table.containsValue(30));

        // Checking for the Value '40'
        System.out.println("Is the value '40' present? " +
        hash_table.containsValue(40));
    }
}

Output:

Initial Mappings are: {You=30, Welcomes=25, 4=15, Geeks=20}
Is the value '10' present? false
Is the value '30' present? true
Is the value '40' present? false