The java.util.Hashtable is used to create a set of key elements in the hash table. It basically returns a set view of the keys, or we can create a new set and store the key elements in them.
Syntax:
public Set<K> keySet()
K : type of the Keys in the hash table
Parameters: The method does not take any parameter.
Return Value: The method returns a set having the keys of the hash table.
Below programs are used to illustrate the working of java.util.Hashtable.keySet() Method:
Example 1:Â
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Java
// Java code to illustrate the keySet() method// to get Set view of Keys from a Hashtable.  import java.util.Enumeration;import java.util.Iterator;import java.util.Hashtable;import java.util.Set;  public class Example1 {      public static void main(String[] args)    {          // Creating an empty Hashtable        Hashtable<String, String> hash_t            = new Hashtable<String, String>();          // Add mappings into the table        hash_t.put("1", "Geeks");        hash_t.put("2", "For");        hash_t.put("3", "Geeks");          // Getting a Set of keys using        // keySet() method of Hashtable class        Set hash_set = hash_t.keySet();          System.out.println(            "Set created from Hashtable Keys contains :");          // Iterating through the Set of keys        Iterator itr = hash_set.iterator();        while (itr.hasNext())            System.out.println(itr.next());    }} |
Output
Set created from Hashtable Keys contains : 3 2 1
Example 2:
Java
// Java code to illustrate the keySet() method// to get Set view of Keys from a Hashtable.  import java.util.Enumeration;import java.util.Iterator;import java.util.Hashtable;import java.util.Set;  public class Example2 {      public static void main(String[] args)    {          // Creating an empty Hashtable        Hashtable<String, String> hash_t            = new Hashtable<String, String>();          // Inserting elements into the table        hash_t.put("Geeks", "1");        hash_t.put("For", "2");        hash_t.put("geeks", "3");          // Getting a Set of keys using        // keySet() method of Hashtable class        Set hash_set = hash_t.keySet();          System.out.println(            "Set created from Hashtable Keys contains :");          // Iterating through the Set of keys        Iterator itr = hash_set.iterator();        while (itr.hasNext())            System.out.println(itr.next());    }} |
Output
Set created from Hashtable Keys contains : For Geeks geeks
 Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.
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