Java中的WeakHashMap containsKey()方法

Java.util.WeakHashMap.containsKey() 方法用于检查特定键是否被映射到 WeakHashMap 中。它将键元素作为参数，如果该元素在映射中映射，则返回 True。

句法：

Weak_Hash_Map.containsKey(key_element)

参数：该方法仅采用一个参数key_element ，该参数引用应该在映射中检查其映射的键。

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

以下程序用于说明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 weak_hash = new WeakHashMap();
  
        // 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 weak_hash = new WeakHashMap();
  
        // 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：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。