I don't believe that programming is something you need to just get. I've seen a lot of people struggle on assignments like these as a TA. Usually, it's that they're missing certain concepts, but they don't know which ones and they can't debug themselves. If you know 70% of basic Java, you won't be able to create a working solution. You'll get tripped up on a type mismatch error that just makes you bonkers until you give up because you don't know what the error message means or you tried to make a templated array rather than an Object array and casting it to a templated array or whatnot.

There are lots of little pitfalls in programming that are just terrible. In C, you can just walk off the end of an array (or the beginning). In Java, you can store an object in an array and then modify that object in both the array copy and the one you have in a regular variable because Java works by reference, not by copy. A lot of the time, you just need someone who is a lot more learned in programming to notice that. It's not that you don't get a concept like object references, it's that if it's not in your mind, you don't notice when your code does it and it takes a long time for these things to really get into your mind to the point that you catch them fast.

And most people give up. You get hit enough times with silly things like these and you just want out unless you're truly dedicated. I know when I was learning, I hit all the trap doors. It's why I noticed them when other students made them. Heck, back in the old days of Java, you could easily screw up things like int vs. Integer and not notice it - especially since a lot of professors might not make a distinction because for veteran programmers, we know that pitfall, but also because its place is at the start where students get inundated with syntax and such a distinction might go unnoticed (or abbreviated as int in notes).

I would think schools should hire more TAs to help students through those pitfalls except that most students like to do assignments at the last minute where these errors become the source of the mind-breaking stress.