Java ConcurrentHashMap containsKey() Method

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The ConcurrentHashMap.containsKey() method in Java is used to check if a specified key is present in a ConcurrentHashMap. 

Table of Contents

1. Introduction
2. containsKey Method Syntax
3. Examples
   • Checking for Keys in a ConcurrentHashMap
   • Handling Non-Existent Keys
4. Real-World Use Case
   • Example: Verifying User Sessions
5. Conclusion

Introduction

The ConcurrentHashMap.containsKey() method is a member of the ConcurrentHashMap class in Java. It allows you to check if a specific key is present in the map. 

The ConcurrentHashMap class is part of the java.util.concurrent package, designed for high concurrency and scalability.

containsKey() Method Syntax

The syntax for the containsKey method is as follows:

public boolean containsKey(Object key)

• The method takes one parameter:
  • key of type Object, which represents the key to be checked for presence in the map.
• The method returns true if the key is present in the map, and false otherwise.

Examples

Checking for Keys in a ConcurrentHashMap

The containsKey method can be used to check for the presence of keys in a ConcurrentHashMap.

Example

import java.util.concurrent.ConcurrentHashMap;

public class ContainsKeyExample {
    public static void main(String[] args) {
        // Creating a ConcurrentHashMap with String keys and Integer values
        ConcurrentHashMap<String, Integer> people = new ConcurrentHashMap<>();

        // Adding entries to the ConcurrentHashMap
        people.put("Ravi", 25);
        people.put("Priya", 30);
        people.put("Vijay", 35);

        // Checking for the presence of keys
        boolean hasRavi = people.containsKey("Ravi");
        boolean hasAnita = people.containsKey("Anita");

        // Printing the results
        System.out.println("Contains key 'Ravi': " + hasRavi);
        System.out.println("Contains key 'Anita': " + hasAnita);
    }
}

Output:

Contains key 'Ravi': true
Contains key 'Anita': false

Handling Non-Existent Keys

The containsKey method returns false if the specified key is not present in the ConcurrentHashMap.

Example

import java.util.concurrent.ConcurrentHashMap;

public class NonExistentKeyExample {
    public static void main(String[] args) {
        // Creating a ConcurrentHashMap with String keys and Integer values
        ConcurrentHashMap<String, Integer> people = new ConcurrentHashMap<>();

        // Adding entries to the ConcurrentHashMap
        people.put("Ravi", 25);
        people.put("Priya", 30);

        // Checking for the presence of a non-existent key
        boolean hasVijay = people.containsKey("Vijay");

        // Printing the result
        System.out.println("Contains key 'Vijay': " + hasVijay);
    }
}

Output:

Contains key 'Vijay': false

Real-World Use Case

Example: Verifying User Sessions

A common real-world use case for ConcurrentHashMap is managing user session data and verifying if a user's session exists.

Example

import java.util.concurrent.ConcurrentHashMap;

public class UserSessionStore {
    public static void main(String[] args) {
        // Creating a ConcurrentHashMap to manage user sessions
        ConcurrentHashMap<String, String> userSessions = new ConcurrentHashMap<>();

        // Adding user sessions to the ConcurrentHashMap
        userSessions.put("Ravi", "Session1");
        userSessions.put("Priya", "Session2");
        userSessions.put("Vijay", "Session3");

        // Checking for the presence of user sessions
        boolean sessionExists = userSessions.containsKey("Ravi");
        boolean sessionNonExists = userSessions.containsKey("Anita");

        // Printing the results
        System.out.println("Session exists for Ravi: " + sessionExists);
        System.out.println("Session exists for Anita: " + sessionNonExists);


}

Output:

Session exists for Ravi: true
Session exists for Anita: false

In this example, ConcurrentHashMap is used to manage user session data, and the containsKey method is employed to verify the existence of specific user sessions in a thread-safe manner.

Conclusion

The ConcurrentHashMap.containsKey() method in Java provides a way to check for the presence of specific keys in a ConcurrentHashMap in a thread-safe manner. By understanding how to use this method, you can efficiently manage collections of key-value pairs in your Java applications, especially in concurrent environments. The method allows you to handle the presence and absence of keys, making it a versatile tool for data management in multi-threaded scenarios.