Hashtable keys() Method in Java

As we all know enumeration defines java class type so do enumerations can have constructors, methods, and instance variables. The java.util.Hashtable.keys() method of Hashtable class in Java is used to get the enumeration of the keys present in the hashtable.

Illustration:

Syntax:

public Enumeration<K> keys()
Enumeration enu = Hash_table.keys();

Return value: An enumeration of the keys of the Hashtable.

Example 1:

Java

// Java Program to Illustrate keys() method
// of Hashtable class

// Importing utility classes
import java.util.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] args)
    {
        // Creating an empty Hashtable
        // Declaring object of integer and string type
        Hashtable<Integer, String> hash_table
            = new Hashtable<Integer, String>();

        // Inserting elements into the table
        // using put() method

        // Custom input elements
        hash_table.put(10, "Geeks");
        hash_table.put(15, "4");
        hash_table.put(20, "Geeks");
        hash_table.put(25, "Welcomes");
        hash_table.put(30, "You");

        // Print and display all entered elements in object
        System.out.println("The Table is: " + hash_table);

        // Creating an empty enumeration to store
        Enumeration enu = hash_table.keys();

        // Display message
        System.out.println("The enumeration of keys are:");

        // Condition holds true till there is single element
        // remaining using hasMoreElements() method
        while (enu.hasMoreElements()) {

            // Displaying the Enumeration
            System.out.println(enu.nextElement());
        }
    }
}

Output:

The Table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
The enumeration of keys are:
10
20
30
15
25

Example 2:

Java

// Java Program to illustrate  keys() method
// of Hashtable class

// Importing utility classes
import java.util.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] args)
    {
        // Creating an empty Hashtable
        // Declaring object of string and integer type
        Hashtable<String, Integer> hash_table
            = new Hashtable<String, Integer>();

        // Inserting elements into the table
        // using put() method
        hash_table.put("Geeks", 10);
        hash_table.put("4", 15);
        hash_table.put("Geeks", 20);
        hash_table.put("Welcomes", 25);
        hash_table.put("You", 30);

        // Displaying the Hashtable
        System.out.println("The Table is: " + hash_table);

        // Creating an empty enumeration to store
        Enumeration enu = hash_table.keys();

        // Display message
        System.out.println("The enumeration of keys are:");

        // Condition holds true till there is single element
        // remaining via hasMoreElements() method
        while (enu.hasMoreElements()) {

            // Displaying the enumeration
            System.out.println(enu.nextElement());
        }
    }
}

Output:

The Table is: {You=30, Welcomes=25, 4=15, Geeks=20}
The enumeration of keys are:
You
Welcomes
4
Geeks