ConcurrentHashMap containsKey() Method in Java

Last Updated : 14 Sep, 2018

The java.util.concurrent.ConcurrentHashMap.containsKey() method is an in-built function in Java which accepts a parameter and checks whether it is a key in this map.

Syntax:

chm.containsKey(Object key_element)

Parameters: The method accepts a single parameter key_element of object type which is to be checked for whether it is a key or not.

Return Value: The method returns true if the specified key_element is a key of this map and false otherwise.

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

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

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

/* 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."); 
        } 
    } 
} 

Output:

105 is not a key.
100 is a key.

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

/* 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."); 
        } 
    } 
} 

Output:

GFG is a key.
Geek is not a key.

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

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