Java LinkedHashMap containsKey()方法及示例

java.util.LinkedHashMap.containsKey()方法是用来检查一个特定的键是否被映射到LinkedHashMap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

Linked_Hash_Map.containsKey(key_element)

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

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

例子1： 将字符串值映射到整数键。

// 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 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。