Java HashMap containsKey()用法及代碼示例

java.util.HashMap.containsKey()方法用於檢查特定鍵是否已映射到HashMap中。它使用key元素作為參數，如果該元素在映射中映射，則返回True。

用法:

Hash_Map.containsKey(key_element)

參數：該方法僅采用一個參數key_element，該參數表示應該在映射內檢查其映射的鍵。

返回值：如果檢測到鍵的存在，則該方法返回boolean true，否則返回false。

以下程序用於說明java.util.HashMap.containsKey()方法的用法：
示例1:將字符串值映射到整數鍵。

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

輸出：

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

示例2:將整數值映射到字符串鍵。

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

輸出：

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

注意：可以對具有不同數據類型的變化和組合的任何類型的映射執行相同的操作。

相關用法

注：本文由純淨天空篩選整理自Chinmoy Lenka大神的英文原創作品 HashMap containsKey() Method in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。