Java中LinkedHashMap containsKey（）方法及其示例-yiteyi-C++库

爪哇。util。LinkedHashMap。containsKey（）方法用于检查特定密钥是否映射到LinkedHashMap。它将key元素作为参数，如果该元素映射到映射中，则返回True。 语法：

null

Linked_Hash_Map.containsKey(key_element)

参数： 该方法只需要一个参数 关键元素 它指的是应该在映射中检查其映射的密钥。

返回类型： 如果检测到密钥存在，则该方法返回布尔值true，否则返回false。

例1： 将字符串值映射到整数键。

JAVA

                         // Java code to illustrate the containsKey() method                       
                         import                                     java.util.*;                       
                                   
                         public                                     class                                     Linked_Hash_Map_Demo {                       
                                                 public                                     static                                     void                                     main(String[] args)                       
                                                 {                       
                                   
                                                 // Creating an empty LinkedHashMap                       
                                                 LinkedHashMap<Integer, String> li_hash_map =                       
                                                 new                                     LinkedHashMap<Integer, String>();                       
                                   
                                                 // Mapping string values to int keys                       
                                                 li_hash_map.put(                                     10                                     ,                                     "Geeks"                                     );                       
                                                 li_hash_map.put(                                     15                                     ,                                     "4"                                     );                       
                                                 li_hash_map.put(                                     20                                     ,                                     "Geeks"                                     );                       
                                                 li_hash_map.put(                                     25                                     ,                                     "Welcomes"                                     );                       
                                                 li_hash_map.put(                                     30                                     ,                                     "You"                                     );                       
                                   
                                                 // Displaying the LinkedHashMap                       
                                                 System.out.println(                                     "Initial Mappings are: "                                     + li_hash_map);                       
                                   
                                                 // Checking for the key_element '20'                       
                                                 System.out.println(                                     "Is the key '20' present? "                                     +                       
                                                 li_hash_map.containsKey(                                     20                                     ));                       
                                   
                                                 // Checking for the key_element '5'                       
                                                 System.out.println(                                     "Is the key '5' present? "                                     +                       
                                                 li_hash_map.containsKey(                                     5                                     ));                       
                                                 }                       
                         }                       

输出：

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

例2： 将整数值映射到字符串键。

JAVA

                         // Java code to illustrate the containsKey() method                       
                         import                                     java.util.*;                       
                                   
                         public                                     class                                     Hash_Map_Demo {                       
                                                 public                                     static                                     void                                     main(String[] args)                       
                                                 {                       
                                   
                                                 // Creating an empty LinkedHashMap                       
                                                 LinkedHashMap<String, Integer> li_hash_map =                       
                                                 new                                     LinkedHashMap<String, Integer>();                       
                                   
                                                 // Mapping int values to string keys                       
                                                 li_hash_map.put(                                     "Geeks"                                     ,                                     10                                     );                       
                                                 li_hash_map.put(                                     "4"                                     ,                                     15                                     );                       
                                                 li_hash_map.put(                                     "Geeks"                                     ,                                     20                                     );                       
                                                 li_hash_map.put(                                     "Welcomes"                                     ,                                     25                                     );                       
                                                 li_hash_map.put(                                     "You"                                     ,                                     30                                     );                       
                                   
                                                 // Displaying the LinkedHashMapHashMap                       
                                                 System.out.println(                                     "Initial Mappings are: "                                     + li_hash_map);                       
                                   
                                                 // Checking for the key_element 'Welcomes'                       
                                                 System.out.println(                                     "Is the key 'Welcomes' present? "                                     +                       
                                                 li_hash_map.containsKey(                                     "Welcomes"                                     ));                       
                                   
                                                 // Checking for the key_element 'World'                       
                                                 System.out.println(                                     "Is the key 'World' present? "                                     +                       
                                                 li_hash_map.containsKey(                                     "World"                                     ));                       
                                                 }                       
                         }                       

输出：

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

注：相同的操作可以在不同数据类型的变化和组合的任何类型的映射中执行。

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