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:
20
25
10
30
15

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:
4
Geeks
You
Welcomes