Java WeakHashMap containsKey()方法

java.util.WeakHashMap.containsKey()方法是用来检查一个特定的键是否被映射到WeakHashMap中。它以键元素为参数，如果该元素被映射到地图中，则返回True。

语法

Weak_Hash_Map.containsKey(key_element)

参数： 该方法只需要一个参数key_element，指的是要在地图中检查其映射的键。

返回值： 如果检测到键的存在，该方法返回布尔值true，否则返回false。

下面的程序用来说明java.util.WeakHashMap.containsKey()方法的工作：
程序1： 将字符串值映射到整数键。

// Java code to illustrate the containsKey() 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);
  
        // Checking for the key_element '20'
        System.out.println("Is the key '20' present? " + 
                                  weak_hash.containsKey(20));
  
        // Checking for the key_element '5'
        System.out.println("Is the key '5' present? " + 
                                   weak_hash.containsKey(5));
    }
}

输出：

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
Is the key '20' present? true
Is the key '5' present? false

程序2： 将整数值映射到字符串键。

// Java code to illustrate the containsKey() 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);
  
        // Checking for the key_element 'Welcomes'
        System.out.println("Is the key 'Welcomes' present? " + 
                                  weak_hash.containsKey("Welcomes"));
  
        // Checking for the key_element 'World'
        System.out.println("Is the key 'World' present? " + 
                                      weak_hash.containsKey("World"));
    }
}

输出：

Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
Is the key 'Welcomes' present? true
Is the key 'World' present? false

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。