Java IdentityHashMap containsKey() Method

The IdentityHashMap.containsKey() method in Java is used to check if the map contains a mapping for the specified key. 

Table of Contents

1. Introduction
2. containsKey Method Syntax
3. Examples
   • Basic Usage of containsKey Method
   • Checking for Non-Existent Keys
4. Real-World Use Case
   • Example: Managing Active User Sessions
5. Conclusion

Introduction

The IdentityHashMap.containsKey() method is a member of the IdentityHashMap class in Java. This class uses reference equality (==) instead of object equality (equals()) when comparing keys. The containsKey method checks if the map contains a mapping for the specified key.

containsKey() Method Syntax

The syntax for the containsKey method is as follows:

public boolean containsKey(Object key)

• Parameters:
  • key: The key whose presence in this map is to be tested.
• Returns: true if this map contains a mapping for the specified key.

Examples

Basic Usage of containsKey Method

The containsKey method can be used to check if a specified key is present in an IdentityHashMap.

Example

import java.util.IdentityHashMap;

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

        // Adding key-value pairs to the IdentityHashMap
        map.put("Ravi", 25);
        map.put("Priya", 30);
        map.put("Vijay", 35);

        // Checking if specific keys are present in the IdentityHashMap
        boolean containsRavi = map.containsKey("Ravi");
        boolean containsAnita = map.containsKey("Anita");

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

Output:

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

Checking for Non-Existent Keys

If the specified key is not found in the IdentityHashMap, the containsKey method returns false.

Example

import java.util.IdentityHashMap;

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

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

        // Checking if a non-existent key is present in the IdentityHashMap
        boolean containsVijay = map.containsKey("Vijay");

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

Output:

Contains key 'Vijay': false

Real-World Use Case

Example: Managing Active User Sessions

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

Example

import java.util.IdentityHashMap;

public class ActiveUserSessionManager {
    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<>();
        sessionMap.put(session1, "Active");
        sessionMap.put(session2, "Inactive");

        // Checking if specific user sessions are active
        boolean containsSession1 = sessionMap.containsKey(session1);
        UserSession session3 = new UserSession("S3", "Vijay");
        boolean containsSession3 = sessionMap.containsKey(session3);

        // Printing the results
        System.out.println("Contains session 1: " + containsSession1);
        System.out.println("Contains session 3: " + containsSession3);
    }
}

Output:

Contains session 1: true
Contains session 3: false

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

Conclusion

The IdentityHashMap.containsKey() method in Java provides a way to check if the map contains a mapping for the specified key, 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.