Where to add magic numbers in my project? [closed]

I have a lot of magic numbers and strings in my project and I would like to replace them with constants. The thing is I remember I used, a lot of time ago, a class to hold all the constants that I would call in the code statically. It is a university project and I need to use Java design patterns.

I would like to know what's the best way to write the constants given the fact that many magic numbers are used across different classes, so I don't want to declare constants locally in each class.

I've read about resource files implemented via singleton classes, but I can't figure out why using a singleton class that makes calls to it longer than needed.

I'm writing code in Java for the server and Android for the client in case you need this info.