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.
