Java practice?

Question

Java

Hello. Probably, such questions tortured you, but I’ll ask)
I read the first volume of Schildt on Java and I wonder where to get puzzles for myself to solve?
And experienced people need advice, but how best to move? There is an understanding of the code (at least on the Internet and books, I understand what I see). The pet project is still out of reach for me due to the fact that I do not know Java Core firmly, and Spring has not yet begun to learn.
And actually one more question, what is meant by Java Core?
I understand that this is from data types to annotations, multithreading and exceptions, but I would like more details. Maybe someone will formulate a task or throw a link to tasks in order to understand to what extent I know this Java Core.
Before Java, there was little experience in other PLs.
I liked Java, its prevalence, wide applicability, and the fact that you can write on a bucket) In the future, I think I’ll try it under a bucket, but first Java Core, Spring Maven, etc., delve into home projects, and then everything else.
Schildt writes interestingly. Some places are not very intelligible, you have to google. I didn't really understand the annotations. More precisely, I did not really understand why. But I'm not worried, because before that the rest need to be mastered.
I read Fine, well, that's it. His book Programming for Kids is strange. 50 pages about Core and then immediately Swing. I learned much more from Schildt, although I knew half of these books even without them.

Answer 1

To learn how to program, you have to program.
If you want to learn how to program for android, then come up with a pet project and try to implement it.
Or try to get a job as a junior.
There will be a lot of practice and external motivation :-)