Loop through a HashMap using an Iterator in Java

An Iterator can be used to loop through a HashMap. The method hasNext( ) returns true if there are more elements in HashMap and false otherwise. The method next( ) returns the next key element in the HashMap and throws the exception NoSuchElementException if there is no next element.

A program that demonstrates this is given as follows.

Example

 Live Demo

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
public class Demo {
   public static void main(String[] args) {
      Map student = new HashMap();
      student.put("101", "Harry");
      student.put("102", "Amy");
      student.put("103", "John");
      student.put("104", "Susan");
      student.put("105", "James");
      Iterator i = student.keySet().iterator();
      while (i.hasNext()) {
         String key = (String) i.next();
         System.out.println("\nRoll Number: " + key);
         System.out.println("Name: " + student.get(key));
      }
   }
}

Output

The output of the above program is as follows −

Roll Number: 101
Name: Harry

Roll Number: 102
Name: Amy

Roll Number: 103
Name: John

Roll Number: 104
Name: Susan

Roll Number: 105
Name: James

Now let us understand the above program.

The HashMap is created and HashMap.put() is used to add the entries to the HashMap. Then the HashMap entries i.e. the keys and the values are displayed using an iterator which makes use of the Iterator interface. A code snippet which demonstrates this is as follows

Map student = new HashMap();
student.put("101", "Harry");
student.put("102", "Amy");
student.put("103", "John");
student.put("104", "Susan");
student.put("105", "James");
Iterator i = student.keySet().iterator();
while (i.hasNext()) {
   String key = (String) i.next();
   System.out.println("\nRoll Number: " + key);
   System.out.println("Name: " + student.get(key));
}

Ankith Reddy

Published on 18-Jan-2019 10:35:00