Java ConcurrentHashMap isEmpty() Method

The ConcurrentHashMap.isEmpty() method in Java is used to check if a ConcurrentHashMap is empty.

Table of Contents

1. Introduction
2. isEmpty Method Syntax
3. Examples
   • Checking if a ConcurrentHashMap is Empty
   • After Adding and Removing Entries
4. Real-World Use Case
   • Example: Monitoring User Session Activity
5. Conclusion

Introduction

The ConcurrentHashMap.isEmpty() method is a member of the ConcurrentHashMap class in Java. It allows you to determine whether the map contains any key-value pairs. The ConcurrentHashMap class is part of the java.util.concurrent package, designed for high concurrency and scalability.

isEmpty() Method Syntax

The syntax for the isEmpty method is as follows:

public boolean isEmpty()

• The method takes no parameters.
• The method returns a boolean value:
  • true if the map contains no key-value pairs.
  • false if the map contains one or more key-value pairs.

Examples

Checking if a ConcurrentHashMap is Empty

The isEmpty method can be used to check if a ConcurrentHashMap is empty.

Example

import java.util.concurrent.ConcurrentHashMap;

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

        // Checking if the ConcurrentHashMap is empty
        boolean isEmpty = people.isEmpty();

        // Printing the result
        System.out.println("Is the ConcurrentHashMap empty? " + isEmpty);
    }
}

Output:

Is the ConcurrentHashMap empty? true

After Adding and Removing Entries

The isEmpty method reflects changes in the map after adding or removing entries.

Example

import java.util.concurrent.ConcurrentHashMap;

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

        // Checking if the ConcurrentHashMap is empty initially
        System.out.println("Is the ConcurrentHashMap empty initially? " + people.isEmpty());

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

        // Checking if the ConcurrentHashMap is empty after adding entries
        System.out.println("Is the ConcurrentHashMap empty after adding entries? " + people.isEmpty());

        // Removing entries
        people.clear();

        // Checking if the ConcurrentHashMap is empty after removing entries
        System.out.println("Is the ConcurrentHashMap empty after removing entries? " + people.isEmpty());
    }
}

Output:

Is the ConcurrentHashMap empty initially? true
Is the ConcurrentHashMap empty after adding entries? false
Is the ConcurrentHashMap empty after removing entries? true

Real-World Use Case

Example: Monitoring User Session Activity

A common real-world use case for ConcurrentHashMap is managing user session data and checking if there are any active sessions.

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", "Active");
        userSessions.put("Priya", "Inactive");

        // Checking if there are any user sessions
        boolean areSessionsEmpty = userSessions.isEmpty();

        // Printing the number of user sessions
        System.out.println("Are there any user sessions? " + areSessionsEmpty);

        // Clearing all sessions
        userSessions.clear();

        // Checking if there are any user sessions after clearing
        boolean areSessionsEmptyAfterClear = userSessions.isEmpty();

        // Printing the result
        System.out.println("Are there any user sessions after clearing? " + areSessionsEmptyAfterClear);
    }
}

Output:

Are there any user sessions? false
Are there any user sessions after clearing? true

In this example, ConcurrentHashMap is used to manage user session data, and the isEmpty method is employed to check if there are any active user sessions in a thread-safe manner.

Conclusion

The ConcurrentHashMap.isEmpty() method in Java provides a way to check if a ConcurrentHashMap contains any key-value pairs 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 monitor the state of the map, making it a versatile tool for data management in multi-threaded scenarios.