Java IdentityHashMap values() Method

The IdentityHashMap.values() method in Java returns a collection view of the values contained in the map. 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.values() can be used effectively.

Table of Contents

1. Introduction
2. values Method Syntax
3. Examples
   • Basic Usage of values Method
   • Iterating Over Values
4. Real-World Use Case
   • Example: Displaying User Session Statuses
5. Conclusion

Introduction

The IdentityHashMap.values() method is a member of the IdentityHashMap class in Java. This class uses reference equality (==) instead of object equality (equals()) when comparing keys. The values method returns a collection view of the values contained in the map.

values() Method Syntax

The syntax for the values method is as follows:

public Collection<V> values()

• Parameters: This method does not take any parameters.
• Returns: A collection view of the values contained in this map.

Examples

Basic Usage of values Method

The values method can be used to get a collection view of the values contained in the IdentityHashMap.

Example

import java.util.IdentityHashMap;
import java.util.Collection;

public class IdentityHashMapValuesExample {
    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);

        // Getting the collection view of the values
        Collection<Integer> values = map.values();

        // Printing the collection view of the values
        System.out.println("IdentityHashMap Values: " + values);
    }
}

Output:

IdentityHashMap Values: [25, 30, 35]

Iterating Over Values

You can iterate over the values in the IdentityHashMap using the collection view returned by the values method.

Example

import java.util.IdentityHashMap;
import java.util.Collection;

public class IdentityHashMapIterateValuesExample {
    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);

        // Getting the collection view of the values
        Collection<Integer> values = map.values();

        // Iterating over the values
        for (Integer value : values) {
            System.out.println("Value: " + value);
        }
    }
}

Output:

Value: 25
Value: 30
Value: 35

Real-World Use Case

Example: Displaying User Session Statuses

A common real-world use case for IdentityHashMap.values() is displaying the statuses of user sessions in a web application where reference equality is required.

Example

import java.util.IdentityHashMap;
import java.util.Collection;

public class UserSessionStatusDisplay {
    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");
        UserSession session3 = new UserSession("S3", "Vijay");

        // Creating an IdentityHashMap to manage user sessions
        IdentityHashMap<UserSession, String> sessionMap = new IdentityHashMap<>();
        sessionMap.put(session1, "Active");
        sessionMap.put(session2, "Inactive");
        sessionMap.put(session3, "Active");

        // Getting the collection view of the values (statuses)
        Collection<String> statuses = sessionMap.values();

        // Displaying the user session statuses
        for (String status : statuses) {
            System.out.println("Session Status: " + status);
        }
    }
}

Output:

Session Status: Active
Session Status: Inactive
Session Status: Active

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

Conclusion

The IdentityHashMap.values() method in Java provides a way to get a collection view of the values contained in the map, 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.