Java ConcurrentHashMap keySet()用法及代码示例

Java中的ConcurentHashMap类的keySet()方法用于从哈希映射中包含的关键元素中创建一个集合。它本质上返回键的集合视图，或者我们可以创建一个新集合并将键元素存储在其中。

用法:

ConcurrentHashMap.keySet()

参数：该方法不带任何参数。

返回值：该方法返回一个具有哈希映射键的集合。

以下程序用于说明keySet()方法的用法：

示例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]

示例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：可以对具有不同数据类型的变化和组合的任何类型的映射执行相同的操作。

相关用法

注：本文由纯净天空筛选整理自Chinmoy Lenka大神的英文原创作品 ConcurrentHashMap keySet() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。