Home » Core Java » util » HashMap » Get Set view of HashMap keys example

About Byron Kiourtzoglou

Byron Kiourtzoglou
Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Get Set view of HashMap keys example

This is an example of how to get a Set view of HashMap keys. Getting a Set view of HashMap keys implies that you should:

  • Create a new HashMap.
  • Populate the hashMap with elements, with the put(K key, V value) API method of HashMap.
  • Invoke the keySet() API method of HashMap to get a Set containing all keys in the hashMap. The key set is backed by the HashMap, thus elements removed from the key set will also be removed from the originating HashMap. Nevertheless it is not permitted to add an element to the resultant key set and
    UnsupportedOperationException exception will be thrown in case we try to.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;

import java.util.HashMap;
import java.util.Set;
 
public class KeySetHashMap {
 
  public static void main(String[] args) {
 
    // Create a HashMap and populate it with elements
    HashMap hashMap = new HashMap();
    hashMap.put("key_1","value_1");
    hashMap.put("key_2","value_2");
    hashMap.put("key_3","value_3");
 
    /* 

Set keySet() operation returns a Set containing all keys in HashMap. 

The key set is backed by the HashMap thus elements removed from the 

key set will also be removed from the originating HashMap. 

Nevertheless it is not permitted to add an element to the resultant key set and 

java.lang.UnsupportedOperationException exception will be thrown in case we try to.
    */
    Set keySet = hashMap.keySet();

    System.out.println("keySet contains : " + keySet);

    keySet.remove("key_2");

    System.out.println("after removing key_2 from keySet, keySet contains : " + keySet + " hashMap contains : " + hashMap);
  }
}

Output:

keySet contains : [key_3, key_2, key_1]
after removing key_2 from keySet, keySet contains : [key_3, key_1] hashMap contains : {key_3=value_3, key_1=value_1}

 
This was an example of how to get a Set view of HashMap keys in Java.

0 0 vote
Article Rating

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

 

Subscribe
Notify of
guest
The comment form collects your name, email and content to allow us keep track of the comments placed on the website. Please read and accept our website Terms and Privacy Policy to post a comment.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x