Is it possible to implement a hashCode that always returns different values for different objects (without collisions)?

Implementing a hashCode that always returns a unique value for each object without collisions is practically impossible in the general case, especially if the hash space is limited (for example, a 32-bit or 64-bit integer).

Reasons:

• The number of possible objects is often infinite or very large.
• The size of the hash code is limited, so the number of unique values is limited.
• According to Dirichlet's principle, collisions are inevitable with a large number of objects.

If objects are limited in number and their state can be stored, a unique identifier for each object (for example, an auto-incremented ID) can be implemented, but this is no longer a classic hashCode, but a unique ID.

In Java, hashCode is intended for quick computation and distribution of objects across buckets in hash tables, not for guaranteed uniqueness. Therefore, collisions are allowed and handled.

Conclusion: avoiding collisions can only be guaranteed with a limited and pre-known set of objects, or by using large data structures (for example, UUID), but this is not a classic hashCode.