Java ConcurrentHashMap containsValue()用法及代码示例

java.util.concurrent.ConcurrentHashMap.containsValue()方法是Java中的内置函数，该函数接受一个值，如果将一个或多个键映射到指定值，则返回true。此方法遍历整个哈希表。因此，它的函数比containsKey()方法慢得多。

用法:

chm.containsValue(Object val_element)

参数：该方法接受对象类型的单个参数val_element，将检查该对象是否已映射到映射中的任何键。

返回值：如果指定的val_element映射到此映射中的任何键，则该方法返回true，否则返回false。

异常：当指定的value_element为null时，该函数将引发NullPointerException。

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

示例1:该程序涉及将整数值映射到字符串键。

/* 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."); 
        } 
    } 
}

输出：

100 is not mapped.
120 is mapped.

示例2:该程序涉及将字符串值映射到整数键。

/* 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."); 
        } 
    } 
}

输出：

Geeks is mapped.
GfG is not mapped.

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

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注：本文由纯净天空筛选整理自RICHIK BHATTACHARJEE大神的英文原创作品 ConcurrentHashMap containsValue() Method in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。