Java WeakHashMap keySet()方法

Java中的java.util.WeakHashMap.keySet()方法用于从哈希图中包含的键元素中创建一个集合。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

Weak_Hash_Map.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弱哈希图键值的集合。

下面的程序用来说明java.util.WeakHashMap.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 keySet() method
import java.util.*;
  
public class Weak_Hash_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty WeakHashMap
        Map<Integer, String> weak_hash = 
                  new WeakHashMap<Integer, String>();
  
        // Mapping string values to int keys
        weak_hash.put(10, "Geeks");
        weak_hash.put(15, "4");
        weak_hash.put(20, "Geeks");
        weak_hash.put(25, "Welcomes");
        weak_hash.put(30, "You");
  
        // Displaying the WeakHashMap
        System.out.println("Initial Mappings are: " +
                                          weak_hash);
  
        // Using keySet() to get the set view of keys
        System.out.println("The set is: " + 
                                  weak_hash.keySet());
    }
}

输出：

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

程序2： 将整数值映射到字符串键。

// Java code to illustrate the keySet() method
import java.util.*;
  
public class Weak_Hash_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty WeakHashMap
        Map<String, Integer> weak_hash = 
                    new WeakHashMap<String, Integer>();
  
        // Mapping int values to string keys
        weak_hash.put("Geeks", 10);
        weak_hash.put("4", 15);
        weak_hash.put("Geeks", 20);
        weak_hash.put("Welcomes", 25);
        weak_hash.put("You", 30);
  
        // Displaying the WeakHashMap
        System.out.println("Initial Mappings are: " + 
                                           weak_hash);
  
        // Using keySet() to get the set view of keys
        System.out.println("The set is: " + 
                                  weak_hash.keySet());
    }
}

输出：

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

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。