The keys() method of ConcurrentHashMap class in Java is used to get the enumeration of the keys present in the hashmap.
Syntax:
Enumeration enu = ConcurrentHashMap.keys()
Parameters: The method does not take any parameters.
Return value: The method returns an enumeration of the keys of the ConcurrentHashMap.
Below programs are used to illustrate the working of the keys() method:
Program 1:
// Java code to illustrate the keys() method  import java.util.*;import java.util.concurrent.*;  public class ConcurrentHashMapDemo {    public static void main(String[] args)    {          // Creating an empty ConcurrentHashMap        ConcurrentHashMap<Integer, String>            hash_map = new ConcurrentHashMap<Integer,                                             String>();          // Inserting elements into the map        hash_map.put(10, "Geeks");        hash_map.put(15, "4");        hash_map.put(20, "Geeks");        hash_map.put(25, "Welcomes");        hash_map.put(30, "You");          // Displaying the ConcurrentHashMap        System.out.println("The Map is: " + hash_map);          // Creating an empty enumeration to store        Enumeration enu = hash_map.keys();          System.out.println("The enumeration of keys are:");          // Displaying the Enumeration        while (enu.hasMoreElements()) {            System.out.println(enu.nextElement());        }    }} |
Output:
The Map is: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
The enumeration of keys are:
20
25
10
30
15
Program 2:
// Java code to illustrate the keys() method  import java.util.*;import java.util.concurrent.*;  public class ConcurrentHashMapDemo {    public static void main(String[] args)    {          // Creating an empty ConcurrentHashMap        ConcurrentHashMap<String, Integer>            hash_map = new ConcurrentHashMap<String,                                             Integer>();          // Inserting elements into the table        hash_map.put("Geeks", 10);        hash_map.put("4", 15);        hash_map.put("Geeks", 20);        hash_map.put("Welcomes", 25);        hash_map.put("You", 30);          // Displaying the ConcurrentHashMap        System.out.println("The Map is: " + hash_map);          // Creating an empty enumeration to store        Enumeration enu = hash_map.keys();          System.out.println("The enumeration of keys are:");          // Displaying the Enumeration        while (enu.hasMoreElements()) {            System.out.println(enu.nextElement());        }    }} |
Output:
The Map is: {4=15, Geeks=20, You=30, Welcomes=25}
The enumeration of keys are:
4
Geeks
You
Welcomes
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