No clue

My initial attempt was very similar to yours, and I had a similar reaction after looking at the solution. It made no sense to me at all. I seem to remember that a lot of the past tasks that involved working with generics, people would frequently comment on the task page something along the lines of "well, I passed validation, but I don't have any idea what the code does."

Before you dive into wildcards, a general overview of generics is quite helpful. Why nobody thinks of the Oracle tutorials I don't know, but they helped me a lot. Then there is Angelika Langer. She has an extensive FAQ about generics. Even better is the tutorial but that's in german. And I fully agree with Guadalupe. The multithreading quest is hard enough but collections is frustrating. My favorite is somewhere around task3404 (if it's not that), recursive decomposition of mathematical expressions.

I would recommend that you hold off on Collections now and go do MultiThread first. I did the same thing at 20 and did Collections. I stopped after 2-3 levels and did multithreading first instead. I know that they allow you to choose which one to take first, but I can tell you that it feels like the natural flow of the course is basics > core > multithread > collections. Also, I can tell you that a lot of these exercises really confused me when I first tackled them. The more I programmed though the more things started coming together. Actually, there are lots of times when I learned something new that finally connected the dots on something I previously did not understand. I am still learning new things all the time; techniques, algorithms, best practices, new classes, new libraries, etc. The thing is you will never know it all, no matter hard you try. Remember that. For now I recommend keep moving forward with the understanding that you probably wont understand everything now but with continued practice you'll get better. I don't know if you have learned this yet, but that solution is dealing with wildcards. You can look that up.