java.util.Hashtable.put() Method


The put(K key, V value) method is used to map the specified key to the specified value in this hashtable.


Following is the declaration for java.util.Hashtable.put() method.

public V put(K key, V value)


  • key − This is the hashtable key.

  • value − This is the value.

Return Value

The method call returns the previous value of the specified key in this hashtable, or null if it did not have one.


NullPointerException − This is thrown if the key or value is null.


The following example shows the usage of java.util.Hashtable.put()

package com.tutorialspoint;

import java.util.*;

public class HashTableDemo {
   public static void main(String args[]) {
      // create hash table 
      Hashtable htable1 = new Hashtable();      

      // put values in table
      htable1.put(1, "A");
      htable1.put(2, "B");
      htable1.put(3, "C");
      htable1.put(4, "D");

      System.out.println("Initial hash table value: "+htable1);

      // put value at key 4
      String returnval = (String)htable1.put(4,"TP");

      System.out.println("Return value: "+returnval);
      System.out.println("New hash table value: "+htable1); 

Let us compile and run the above program, this will produce the following result.

Initial hash table value: {4=D, 3=C, 2=B, 1=A}
Return value: D
New hash table value: {4=TP, 3=C, 2=B, 1=A}
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