Hashtable remove() Method in Java

Last Updated : 24 Jun, 2021

The java.util.Hashtable.remove() is an inbuilt method of Hashtable class and is used to remove the mapping of any particular key from the table. It basically removes the values for any particular key in the Table.
Syntax:

Hash_Table.remove(Object key)

Parameters: The method takes one parameter key whose mapping is to be removed from the Table.
Return Value: The method returns the value that was previously mapped to the specified key if the key exists else the method returns NULL.
Below programs illustrates the working of java.util.Hashtable.remove() method:
Program 1: When passing an existing key.

Java

// Java code to illustrate the remove() 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>();

        // Inserting elements into the table
        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 Hashtable
        System.out.println("Initial Table is: " + hash_table);

        // Removing the existing key mapping
        String returned_value = (String)hash_table.remove(20);

        // Verifying the returned value
        System.out.println("Returned value is: " + returned_value);

        // Displaying the new table
        System.out.println("New table is: " + hash_table);
    }
}

Output:

Initial Table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Returned value is: Geeks
New table is: {10=Geeks, 30=You, 15=4, 25=Welcomes}

Program 2: When passing a new key.

Java

// Java code to illustrate the remove() 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>();

        // Inserting mappings into the table
        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 Hashtable
        System.out.println("Initial table is: " + hash_table);

        // Removing the new key mapping
        String returned_value = (String)hash_table.remove(50);

        // Verifying the returned value
        System.out.println("Returned value is: " + returned_value);

        // Displaying the new table
        System.out.println("New table is: " + hash_table);
    }
}

Output:

Initial table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Returned value is: null
New table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}

Note: The same operation can be performed with any type of variation and combination of different data types.