Java ConcurrentHashMap containsValue()用法及代碼示例

java.util.concurrent.ConcurrentHashMap.containsValue()方法是Java中的內置函數，該函數接受一個值，如果將一個或多個鍵映射到指定值，則返回true。此方法遍曆整個哈希表。因此，它的函數比containsKey()方法慢得多。

用法:

chm.containsValue(Object val_element)

參數：該方法接受對象類型的單個參數val_element，將檢查該對象是否已映射到映射中的任何鍵。

返回值：如果指定的val_element映射到此映射中的任何鍵，則該方法返回true，否則返回false。

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

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

示例1:該程序涉及將整數值映射到字符串鍵。

/* Java Program to demonstrate containsValue() 
   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); 
  
        // Check whether a key is mapped to 100 
        if (chm.containsValue(100)) { 
            System.out.println("100 is mapped."); 
        } 
        else { 
            System.out.println("100 is not mapped."); 
        } 
  
        // Check whether a key is mapped to 120 
        if (chm.containsValue(120)) { 
            System.out.println("120 is mapped."); 
        } 
        else { 
            System.out.println("120 is not mapped."); 
        } 
    } 
}

輸出：

100 is not mapped.
120 is mapped.

示例2:該程序涉及將字符串值映射到整數鍵。

/* Java Program to demonstrate containsValue() 
   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"); 
        chm.put(103, "Gfg"); 
        chm.put(104, "GFG"); 
  
        // Check whether a key is mapped to Geeks 
        if (chm.containsValue("Geeks")) { 
            System.out.println("Geeks is mapped."); 
        } 
        else { 
            System.out.println("Geeks is not mapped."); 
        } 
  
        // Check whether a key is mapped to GfG 
        if (chm.containsValue("GfG")) { 
            System.out.println("GfG is mapped."); 
        } 
        else { 
            System.out.println("GfG is not mapped."); 
        } 
    } 
}

輸出：

Geeks is mapped.
GfG is not mapped.

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

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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 containsValue() 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。