Java Hashtable put() Method

Last Updated : 22 May, 2025

The Hashtable.put() method is a part of java.util package. This method is used to insert a mapping into a table. This means we can insert a specific key and the value it maps to into a particular table. If an existing key is passed, then the previous value gets replaced by the new value. If a new pair is passed, then the pair gets inserted as a whole.

Syntax of Hashtable put() Method

Below is the syntax of put() method.

Hash_Table.put(key, value)

Parameters:

This method takes two parameters, both of the Object type of the Hashtable.

key: This refers to the key element that needs to be inserted into the table for mapping.
value: This refers to the value that the above key will map to.

Return Value: If an existing key is passed, the previous value gets returned. If a new pair is passed, then null is returned.

Examples of Java Hashtable put() Method

Example 1: In this example, we are going to use the put() method when an existing key is passed.

Java

// Java program to demonstrate Hashtable.put() method
import java.util.*;

public class Geeks {
    public static void main(String[] args) {
        
        // Create an empty Hashtable
        Hashtable<Integer, String> ht = new Hashtable<Integer, String>();
        
        // Insert values into the Hashtable
        ht.put(10, "Geeks");
        ht.put(15, "4");
        ht.put(20, "Geeks");
        ht.put(25, "Welcomes");
        ht.put(30, "You");
        
        System.out.println("Initial table is: " + ht);
        
        // Insert existing key along with a new value
        String returned = ht.put(20, "All");
        
        // Verify the returned value
        System.out.println("Returned value is: " + returned);
        
        System.out.println("New table is: " + ht);
    }
}

Example 2: In this example, let's use the put() method when a new key is passed and we will see what it prints.

Java

// Java program to demonstrate Hashtable.put() method
import java.util.*;

public class Geeks {
    public static void main(String[] args) {
        
        // Create an empty Hashtable
        Hashtable<Integer, String> ht = new Hashtable<Integer, String>();
        
        // Insert values into the Hashtable
        ht.put(10, "Geeks");
        ht.put(15, "4");
        ht.put(20, "Geeks");
        ht.put(25, "Welcomes");
        ht.put(30, "You");
        
        System.out.println("Initial table is: " + ht);
        
        // Insert new key along with a value
        String returned = ht.put(50, "All");
        
        // Verify the returned value
        System.out.println("Returned value is: " + returned);

        System.out.println("New table is: " + ht);
    }
}

Important Points:

The put() method replaces the value if the key is already exists.
The method returns the previous value associated with the key or it returns null if the key was not present.
This method works with any combination of data types as the key and value.

Java Hashtable get() Method

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