Java Hashtable put() Method

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Description

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

Declaration

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

public V put(K key, V value)

Parameters

• 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.

Exception

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

Adding Values to a HashTable of Integer, Integer Pair Example

The following example shows the usage of Java Hashtable put() method to put few values in a Hashtable. We've created a Hashtable object of Integer,Integer pairs. Then few entries are added using put() method and then table is printed.

package com.tutorialspoint;

import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,Integer> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, 1);
      hashtable.put(2, 2);
      hashtable.put(3, 3); 

      System.out.println("Hashtable elements: " + hashtable);
   }    
}

Output

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

Hashtable elements: {3=3, 2=2, 1=1}

Getting Set of Keys of a HashTable of Integer, String Pair Example

The following example shows the usage of Java Hashtable put() method to put few values in a Hashtable. We've created a Hashtable object of Integer,String pairs. Then few entries are added using put() method and then table is printed.

package com.tutorialspoint;

import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,String> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, "tutorials");
      hashtable.put(2, "point");
      hashtable.put(3, "is best"); 

      System.out.println("Hashtable elements: " + hashtable);
   }    
}

Output

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

Hashtable elements: {3=is best, 2=point, 1=tutorials}

Getting Set of Keys of a HashTable of Integer, Object Pair Example

The following example shows the usage of Java Hashtable put() method to put few values in a Hashtable. We've created a Hashtable object of Integer,Student pairs. Then few entries are added using put() method and then table is printed.

package com.tutorialspoint;

import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,Student> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, new Student(1, "Julie"));
      hashtable.put(2, new Student(2, "Robert"));
      hashtable.put(3, new Student(3, "Adam"));

      System.out.println("Hashtable elements: " + hashtable);
   }    
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Output

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

Hashtable elements: {3=[ 3, Adam ], 2=[ 2, Robert ], 1=[ 1, Julie ]}