Java 17: implementing ConcurrentHashMap and Custom Object as Key
I've encountered a strange issue with I'm maintaining legacy code that I need help solving I'm relatively new to this, so bear with me... I'm working with a scenario when using a custom object as a key in a `ConcurrentHashMap` in Java 17. I've implemented a custom class `User` that overrides `hashCode()` and `equals()`, but I'm working with unexpected behavior when trying to retrieve values using instances of this class. Despite using the same properties to create two `User` objects, one object successfully retrieves its associated value while the other does not. Here’s the code for my `User` class: ```java public class User { private String id; private String name; public User(String id, String name) { this.id = id; this.name = name; } @Override public int hashCode() { return Objects.hash(id); } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null || getClass() != obj.getClass()) return false; User user = (User) obj; return Objects.equals(id, user.id); } } ``` I then create a `ConcurrentHashMap` to store `User` objects: ```java ConcurrentHashMap<User, String> userMap = new ConcurrentHashMap<>(); User user1 = new User("1", "Alice"); userMap.put(user1, "First User"); User user2 = new User("1", "Alice"); String value = userMap.get(user2); // Should retrieve "First User" but returns null ``` I expected `userMap.get(user2)` to return "First User" since both `user1` and `user2` have the same `id`. I've confirmed that both `user1` and `user2` have the same hash code, yet the retrieval fails. I've also ensured that there are no other `User` instances with the same `id` in the map at the time of retrieval. What might be going wrong here? Is there something specific about the `ConcurrentHashMap` that I'm missing, or do I need to adjust my implementation of `hashCode()` or `equals()`? Any insights would be greatly appreciated! This is part of a larger web app I'm building. How would you solve this? Is this even possible? I'm coming from a different tech stack and learning Java. Thanks in advance!