Java ConcurrentHashMap containsKey()用法及代碼示例

java.util.concurrent.ConcurrentHashMap.containsKey()方法是Java中的內置函數，它接受參數並檢查其是否為該映射中的鍵。

用法:

chm.containsKey(Object key_element)

參數：該方法接受對象類型的單個參數key_element，將檢查該對象是否為鍵。

返回值：如果指定的key_element是此映射的鍵，則該方法返回true，否則返回false。

異常：當指定的key_element為null時，該函數將引發NullPointerException。

以下程序說明了java.util.concurrent.ConcurrentHashMap.containsKey()方法的用法：

示例1:該程序涉及將字符串值映射到整數鍵。

/* Java Program Demonstrate containsKey() 
   method of ConcurrentHashMap */
  
import java.util.concurrent.*; 
class ConcurrentHashMapDemo { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<Integer, String> chm = 
                 new ConcurrentHashMap<Integer, String>(); 
        chm.put(100, "Geeks"); 
        chm.put(101, "for"); 
        chm.put(102, "Geeks"); 
  
        // Checking whether 105 is a key of the map 
        if (chm.containsKey(105)) { 
            System.out.println("105 is a key."); 
        } 
        else { 
            System.out.println("105 is not a key."); 
        } 
  
        // Checking whether 100 is a key of the map 
        if (chm.containsKey(100)) { 
            System.out.println("100 is a key."); 
        } 
        else { 
            System.out.println("100 is not a key."); 
        } 
    } 
}

輸出：

105 is not a key.
100 is a key.

示例2:該程序涉及將整數值映射到字符串鍵。

/* Java Program Demonstrate containsKey() 
   method of ConcurrentHashMap */
  
import java.util.concurrent.*; 
class ConcurrentHashMapDemo { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<String, Integer> chm =  
                  new ConcurrentHashMap<String, Integer>(); 
        chm.put("Geeks", 120); 
        chm.put("for", 11); 
        chm.put("GeeksforGeeks", 15); 
        chm.put("Gfg", 50); 
        chm.put("GFG", 25); 
  
        // Checking whether GFG is a key of the map 
        if (chm.containsKey("GFG")) { 
            System.out.println("GFG is a key."); 
        } 
        else { 
            System.out.println("GFG is not a key."); 
        } 
  
        // Checking whether Geek is a key of the map 
        if (chm.containsKey("Geek")) { 
            System.out.println("Geek is a key."); 
        } 
        else { 
            System.out.println("Geek is not a key."); 
        } 
    } 
}

輸出：

GFG is a key.
Geek is not a key.

參考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html#containsKey()

相關用法

注：本文由純淨天空篩選整理自RICHIK BHATTACHARJEE大神的英文原創作品 ConcurrentHashMap 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。