Traverse through a HashMap in Java

To traverse through a HashMap, use Iterator. The HashMap class uses a hashtable to implement the Map interface. This allows the execution time of basic operations, such as get( ) and put( ), to remain constant even for large sets.

Following is the code to traverse through a HashMap −

Example

import java.util.*; public class Main {    public static void main(String args[]) {       HashMap hashMap = new HashMap();       hashMap.put("John", new Integer(10000));       hashMap.put("Tim", new Integer(25000));       hashMap.put("Adam", new Integer(15000));       hashMap.put("Katie", new Integer(30000));       hashMap.put("Jacob", new Integer(45000));       hashMap.put("Steve", new Integer(23000));       hashMap.put("Nathan", new Integer(25000));       hashMap.put("Amy", new Integer(27000));       Set set = hashMap.entrySet();       Iterator iterator = set.iterator();       while(iterator.hasNext()) {          Map.Entry map = (Map.Entry)iterator.next();          System.out.print(map.getKey() + ": ");          System.out.println(map.getValue());       }       System.out.println();       System.out.println("Size of IdentintyHashMap: "+hashMap.size());       int bonus = ((Integer)hashMap.get("Amy")).intValue();       hashMap.put("Amy", new Integer(bonus + 5000));       System.out.println("Amy's salary after bonus = " + hashMap.get("Amy"));       int deductions = ((Integer)hashMap.get("Steve")).intValue();       hashMap.put("Steve", new Integer(deductions - 3000));       System.out.println("Steve's salary after deductions = " + hashMap.get("Steve"));    } }

Output

Adam: 15000 Nathan: 25000 Katie: 30000 Steve: 23000 John: 10000 Tim: 25000 Amy: 27000 Jacob: 45000 Size of IdentintyHashMap: 8 Amy's salary after bonus = 32000 Steve's salary after deductions = 20000

You can also traverse through a HashMap using the for-each loop. The keySet() and values() methods are needed here to display the keys and values respectively. Let us now see another example wherein we will be traversing through a HashMap using for-each −

Example

import java.util.HashMap; public class Main {    public static void main(String[] args) {       HashMap<String, String> students = new HashMap<String, String>();       students.put("John", "Maths");       students.put("Tim", "Political Science");       students.put("Steve", "English");       students.put("Nathan", "Science");       for (String s : students.keySet()) {          System.out.println("key= " + s + ", value= " + students.get(s));       }    } }

Output

key= Nathan, value= Science key= Steve, value= English key= John, value= Maths key= Tim, value= Political Science