Método hashtable keys() en Java

Como todos sabemos, la enumeración define el tipo de clase de Java, por lo que las enumeraciones pueden tener constructores, métodos y variables de instancia. El método java.util.Hashtable.keys() de la clase Hashtable en Java se utiliza para obtener la enumeración de las claves presentes en la tabla hash.

Ilustración:

Sintaxis: 

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

Valor de retorno: una enumeración de las claves de Hashtable.

Ejemplo 1:

// 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());
        }
    }
}

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

Ejemplo 2:

// 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());
        }
    }
}

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