Java IdentityHashMap isEmpty() Method

The IdentityHashMap.isEmpty() method in Java is used to check if the map contains no key-value mappings. This guide will cover the method's usage, explain how it works, and provide examples to demonstrate its functionality. We will also cover a real-world use case to show how IdentityHashMap.isEmpty() can be used effectively.

Table of Contents

1. Introduction
2. isEmpty Method Syntax
3. Examples
   • Basic Usage of isEmpty Method
   • Checking after Adding and Removing Elements
4. Real-World Use Case
   • Example: Managing User Sessions
5. Conclusion

Introduction

The IdentityHashMap.isEmpty() method is a member of the IdentityHashMap class in Java. This class uses reference equality (==) instead of object equality (equals()) when comparing keys. The isEmpty method checks if the map contains no key-value mappings.

isEmpty() Method Syntax

The syntax for the isEmpty method is as follows:

public boolean isEmpty()

• Parameters: This method does not take any parameters.
• Returns: true if this map contains no key-value mappings, otherwise false.

Examples

Basic Usage of isEmpty Method

The isEmpty method can be used to check if an IdentityHashMap is empty.

Example

import java.util.IdentityHashMap;

public class IdentityHashMapIsEmptyExample {
    public static void main(String[] args) {
        // Creating an IdentityHashMap
        IdentityHashMap<String, Integer> map = new IdentityHashMap<>();

        // Checking if the IdentityHashMap is empty
        boolean isEmpty = map.isEmpty();

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

Output:

Is IdentityHashMap empty? true

Checking after Adding and Removing Elements

The isEmpty method can be used to check if an IdentityHashMap is empty after adding and removing elements.

Example

import java.util.IdentityHashMap;

public class IdentityHashMapIsEmptyAddRemoveExample {
    public static void main(String[] args) {
        // Creating an IdentityHashMap
        IdentityHashMap<String, Integer> map = new IdentityHashMap<>();

        // Checking if the IdentityHashMap is empty initially
        System.out.println("Initially, is IdentityHashMap empty? " + map.isEmpty());

        // Adding key-value pairs to the IdentityHashMap
        map.put("Ravi", 25);
        map.put("Priya", 30);

        // Checking if the IdentityHashMap is empty after additions
        System.out.println("After additions, is IdentityHashMap empty? " + map.isEmpty());

        // Removing key-value pairs
        map.remove("Ravi");
        map.remove("Priya");

        // Checking if the IdentityHashMap is empty after removals
        System.out.println("After removals, is IdentityHashMap empty? " + map.isEmpty());
    }
}

Output:

Initially, is IdentityHashMap empty? true
After additions, is IdentityHashMap empty? false
After removals, is IdentityHashMap empty? true

Real-World Use Case

Example: Managing User Sessions

A common real-world use case for IdentityHashMap.isEmpty() is managing user sessions in a web application where reference equality is required.

Example

import java.util.IdentityHashMap;

public class UserSessionManager {
    static class UserSession {
        private String sessionId;
        private String userName;

        public UserSession(String sessionId, String userName) {
            this.sessionId = sessionId;
            this.userName = userName;
        }

        @Override
        public String toString() {
            return "UserSession{" +
                    "sessionId='" + sessionId + '\'' +
                    ", userName='" + userName + '\'' +
                    '}';
        }
    }

    public static void main(String[] args) {
        // Creating user sessions
        UserSession session1 = new UserSession("S1", "Ravi");
        UserSession session2 = new UserSession("S2", "Priya");

        // Creating an IdentityHashMap to manage user sessions
        IdentityHashMap<UserSession, String> sessionMap = new IdentityHashMap<>();

        // Checking if the session map is empty initially
        System.out.println("Initially, is session map empty? " + sessionMap.isEmpty());

        // Adding user sessions to the map
        sessionMap.put(session1, "Active");
        sessionMap.put(session2, "Inactive");

        // Checking if the session map is empty after additions
        System.out.println("After additions, is session map empty? " + sessionMap.isEmpty());

        // Removing user sessions from the map
        sessionMap.remove(session1);
        sessionMap.remove(session2);

        // Checking if the session map is empty after removals
        System.out.println("After removals, is session map empty? " + sessionMap.isEmpty());
    }
}

Output:

Initially, is session map empty? true
After additions, is session map empty? false
After removals, is session map empty? true

In this example, IdentityHashMap.isEmpty() is used to manage user sessions, where sessions are identified by reference equality, making it suitable for scenarios where unique object references are crucial.

Conclusion

The IdentityHashMap.isEmpty() method in Java provides a way to check if the map contains no key-value mappings, using reference equality for key comparison. By understanding how to use this method, you can efficiently manage collections of key-value pairs where reference equality is required. This method allows you to utilize the power of IdentityHashMap for various scenarios, making it a versatile tool for managing collections of key-value pairs based on reference equality.