Java - Object reference or identifier?

Question

I am currently creating a big project, and as such I would like to have everything worked out very well and as efficient as possible.

In my project, I have a class called Teams, which contains a HashMap(Integer, Team) of Team objects. Each instance of Team has a unique ID (integer).

There is also an object called Player. Each instance of Player can be assigned to a Team (but not always).

Now, I wonder what the best approach would be to know what Team a Player is assigned to:

-> Store the ID of the team in Player (private int team), this ID is then used to get the Team from the HashMap in Teams.

-> Store a reference to the Team in Player (private Team team)

Does anyone know which is better, and what the most important pro's, con's and dangers are of each?

Thanks!

Answer 1

Use private Team team! Other classes should not need to know the ID of an object unless there is a good reason. Don't implement a Database structure in Java. Java is designed to be Object-based, use it that way.

There are a couple additional reasons you should hold the Team instance:

1. We can assume that your Player will need to access the Team object. It is better to have the instance rather than having to do a lookup.
2. If you hold onto IDs instead of instances, there might not be any reference to an object being held and it could be garbage collected. I know that probably won't happen in your case since you hold all Teams in a Map, but it is still a risk and therefore should be avoided.