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 ]}