Java中的 ConcurrentHashMap keySet() 方法及示例

Java中ConcurentHashMap 类的keySet()方法用于从哈希映射中包含的关键元素创建一个集合。它基本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。

句法：

ConcurrentHashMap.keySet()

参数：该方法不带任何参数。

返回值：该方法返回具有哈希映射键的集合。

下面的程序用于说明 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 hash_map
            = new ConcurrentHashMap();
  
        // 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
            hash_map = new ConcurrentHashMap();
  
        // 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：可以对任何类型的映射执行相同的操作，这些映射具有不同数据类型的变化和组合。