Java ConcurrentHashMap keys()方法及示例

Java中ConcurrentHashMap类的keys()方法用于获取hashmap中存在的键的枚举。

语法

Enumeration enu = ConcurrentHashMap.keys()

参数： 该方法不接受任何参数。

返回值： 该方法返回ConcurrentHashMap的键的枚举值。

下面的程序用来说明keys()方法的工作。

程序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());        }    }}

输出:

The Map is: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}The enumeration of keys are:2025103015

程序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());        }    }}

输出:

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