In this example we shall show you how to get a Set view of Hashtable keys. To get a Set view of Hashtable keys one should perform the following steps:
- Create a new Hashtable.
- Populate the hashtable with elements, using
put(K key, V value)API method of Hashtable. - Invoke
keySet()API method of Hashtable. The method returns a Set that contains all the keys in the Hashtable. The key set is backed by the Hashtable, thus elements removed from the key set will be also removed from the Hashtable.
Note that 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,
as described in the code snippet below.
package com.javacodegeeks.snippets.core;
import java.util.Hashtable;
import java.util.Set;
public class HashtableKeysCollection {
public static void main(String[] args) {
// Create a Hashtable and populate it with elements
Hashtable hashtable = new Hashtable();
hashtable.put("key_1","value_1");
hashtable.put("key_2","value_2");
hashtable.put("key_3","value_3");
hashtable.put("key_4","value_4");
hashtable.put("key_5","value_5");
/*
Set keySet() operation returns a Set containing all keys in Hashtable.
The key set is backed by the Hashtable thus elements removed from the
key set will also be removed from the originating Hashtable.
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 = hashtable.keySet();
System.out.println("keySet contains : " + keySet);
keySet.remove("key_2");
System.out.println("after removing key_2 from keySet, keySet contains : " + keySet + " hashtable contains : " + hashtable);
}
}
Output:
keySet contains : [key_5, key_4, key_3, key_2, key_1]
after removing key_2 from keySet, keySet contains : [key_5, key_4, key_3, key_1] hashtable contains : {key_5=value_5, key_4=value_4, key_3=value_3, key_1=value_1}
This was an example of how to get a Set view of Hashtable keys in Java.
