Hashtable keys() Method in Java

09 Oct, 2021
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 classesimport java.util.*; // Main classpublic 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
 
Example 2:
Java
// Java Program to illustrate  keys() method// of Hashtable class // Importing utility classesimport java.util.*; // Main classpublic 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
 
solankimayank
Java - util package
Java-Collections
Java-HashTable
Java
Java
Java-Collections
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.