To execute the code type in the command line

1. javac Item.java Inventory.java Main.java
2. java Main

(or just create new project in any IDE that supports Java and copy-paste the files)

some highlights:

• I used an enum for Rarity as it has fixed values, also to ensure type safety and easy expansion for new rarities in the future.
• I decided to split the requirments into two main classes: Item and Inventory as Inventory should use Item and they do not have any shared properties
• Items are stored in a Map where keys are rarities and values are ArrayList of items for efficient access, upgrade logic, and expansion. This choice simplifies item grouping and makes the upgrade process more efficient.
• I included some test cases in the Main class
• I did the optional part in a separate class RandomGenerator, because I did not want it to be together with the main functionality of the project(to execute it do javac RandomGenerator.java java RandomGenerator)