ConcurrentHashMap containsKey() Method in Java

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()