Hashtable Iterator example – Java

In this example we will see how to iterate a Hashtable using Iterator. Using Iterator we can display Hashtable key and value separately for each pair of elements.

Example

There are several methods (of both Hashtable class and Iterator interface) used in the below program. Definition and description of each method have been provided in the comment sections of the program.

import java.util.Hashtable;
import java.util.Set;
import java.util.Iterator;

public class IterateHashtable {
 
 public static void main(String[] args) {
 
    String str;
 
    // Creating a Hashtable instance
    Hashtable<String, String> hashtable = new Hashtable<String, String>();
 
    /* Adding key-value pairs to Hashtable
     * public V put(K key, V value): Maps the specified key to the 
     * specified value in this hashtable. Neither the key nor the 
     * value can be null. The value can be retrieved by calling the 
     * get method with a key that is equal to the original key.
     */
    hashtable.put("A", "Apple");
    hashtable.put("B", "Orange");
    hashtable.put("C", "Mango");
    hashtable.put("D", "Banana");
    hashtable.put("E", "Grapes");
 
    System.out.println("Hashtable contains:");
 
    /* public Set<K> keySet(): Returns a Set view of the keys 
     * contained in this map. The set is backed by the map, 
     * so changes to the map are reflected in the set, and 
     * vice-versa.
     */
    Set<String> keys = hashtable.keySet();
 
    //Obtaining iterator over set entries
    Iterator<String> itr = keys.iterator();
 
    //Displaying Key and value pairs
    while (itr.hasNext()) { 
       // Getting Key
       str = itr.next();

       /* public V get(Object key): Returns the value to which 
        * the specified key is mapped, or null if this map 
        * contains no mapping for the key.
        */
       System.out.println("Key: "+str+" & Value: "+hashtable.get(str));
    } 
 }
}

Output:

Hashtable contains:
Key: A & Value: Apple
Key: E & Value: Grapes
Key: D & Value: Banana
Key: C & Value: Mango
Key: B & Value: Orange

References:

1. Hashtable javadoc
2. Iterator javadoc