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ConcurrentHashMap containsValue() Method in Java
  • Last Updated : 14 Sep, 2018

The java.util.concurrent.ConcurrentHashMap.containsValue() method is an in-built function in Java which accepts a value and returns true if one or more keys are mapped to the specified value. This method traverses the entire hashtable. Thus it is a much slower function than containsKey() method.

Syntax:

chm.containsValue(Object val_element)

Parameters: The method accepts a single parameter val_element of object type which is to be checked for whether it is mapped to any key in the map or not.

Return Value: The method returns true if the specified val_element is mapped to any key in this map and false otherwise.

Exception: The function throws NullPointerException when the specified value_element is null.



Below programs illustrate the use of java.util.concurrent.ConcurrentHashMap.containsValue() method :

Program 1: This program involves mapping Integer Values to String Keys.




/* 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.");
        }
    }
}
Output:
100 is not mapped.
120 is mapped.

Program 2: This program involves mapping String Values to Integer Keys.




/* 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.");
        }
    }
}
Output:
Geeks is mapped.
GfG is not mapped.

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

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