How to get the unique ID of an object which overrides hashCode()?

Unveiling the essence of identityHashCode()

When identifying objects in Java, hashCode() often comes into play. But there's another ignored hero in town when you want an object's identity irrespective of hashCode() - System.identityHashCode(obj). It plays a crucial role as a system-level hashCode that turns a blind eye to the hashCode() method you override.

Navigating through limitations

Although System.identityHashCode() could be your go-to method, be mindful that uniqueness is not guaranteed. The JVM's garbage collector might move an object in memory, causing the identity hash code to change.

Moreover, hash collisions, where two objects might have the same identity hash code, may arise. They are few and far between, but the universe might surprise you!

A unique ID generation strategy like an auto-incremented value or a UUID, wrapped with a getId() method in your classes, provides a reliable unique ID fallback net.

Use cases of identityHashCode()

System.identityHashCode() works best when you need to highlight the difference between two objects, regardless of their logical equality. It's often seen walking on debuggers memory lane or in data structures like IdentityHashMap.

Coding your way to consistent unique IDs

Building a concrete object identification

Creating a getId() method in your base interface or abstract class ensures consistent object identification. It's like having IDs issued from the same authority, providing a reliable unique ID across your codebase.

Using getId()

A good old getId() provides a practical way to tell your objects apart, unaffected by any hashCode() shenanigans. It can leverage various ID generation strategies.

The role of Integer.toHexString(hashCode())

The toString() method in Object plays "concatenate the class name with Integer.toHexString(hashCode())". While great for object representation, not so much for uniqueness.

The static variable route

Maintaining a static variable hacked to assign a unique number at instance creation comes with thread safety and scalability concerns in its luggage. Handle with care.

UUID: A Unique ID. Literally.

A UUID is a universally unique identifier and can be summoned using UUID.randomUUID(). It ensures global uniqueness and is often used in distributed systems.