Hashtable keySet() Method in Java with Examples

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:

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.