Java WeakHashMap containsKey()用法及代码示例

java.util.WeakHashMap.containsKey()方法用于检查特定键是否已映射到WeakHashMap中。它使用key元素作为参数，如果该元素在映射中映射，则返回True。

用法:

Weak_Hash_Map.containsKey(key_element)

参数：该方法仅采用一个参数key_element，该参数表示应该在映射内检查其映射的键。

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

以下程序用于说明java.util.WeakHashMap.containsKey()方法的用法：
示例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

示例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：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。

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注：本文由纯净天空筛选整理自Chinmoy Lenka大神的英文原创作品 WeakHashMap containsKey() Method in Java。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。