Java - Convert MIDI to Java data structure (List, Hash Map, ???)

Java - Convert MIDI to Java data structure (List, Hash Map, ???)

First time poster, brand new to Java, and fairly new to programming in
general (so be gentle).
I have what I thought would be a simple project. I want to grab a MIDI
file, read it, and then store the data in some sort of data structure.
Using this site I found an easy way to read the file, which works like a
charm:
Reading MIDI Files
Now I need to figure out a way to grab that output and store it. A Hash
Map doesn't seem ideal since keys need to be unique and a List of type
Object doesn't seem great. Any ideas on what my best option might be. I
suppose I might output it to a text or csv... Thoughts?
Thanks!