Java ConcurrentHashMap keySet()方法及示例

Java中ConcurentHashMap类的keySet()方法是用来创建一个包含在哈希图中的关键元素的集合。它基本上返回一个键的集合视图，或者我们可以创建一个新的集合并将键元素存储在其中。

语法

ConcurrentHashMap.keySet()

参数： 该方法不接受任何参数。

返回值： 该方法返回一个具有哈希图键值的集合。

下面的程序用来说明keySet()方法的工作。

程序1： 将字符串值映射到整数键。

// 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>();
  
        // Mapping string values to int keys
        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 HashMap
        System.out.println("Initial Mappings are: "
                           + hash_map);
  
        // Using keySet() to get the set view of keys
        System.out.println("The set is: "
                           + hash_map.keySet());
    }
}

输出:

Initial Mappings are: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
The set is: [20, 25, 10, 30, 15]

程序2： 将整数值映射到字符串键。

// 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 HashMap
        System.out.println("Initial Mappings are: "
                           + hash_map);
  
        // Using keySet() to get the set view of keys
        System.out.println("The set is: "
                           + hash_map.keySet());
    }
}

输出:

Initial Mappings are: {4=15, Geeks=20, You=30, Welcomes=25}
The set is: [4, Geeks, You, Welcomes]

注意： 同样的操作可以通过不同数据类型的变化和组合对任何类型的Mapping进行操作。