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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Because now there are better alternatives:
Map.of(...). But when that code was written, it wasn't a thing yet.edit: well, at that time, computeIfAbsent would have been an option, tho, iirc.
Could you elaborate? Why shouldn't I used instance initialization blocks?
Good, but I don't know why's that considered a good practice. You should not play with IIBs of standart classes