Just check the documentation and do it yourself. :)
https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html

Where is the good place to learn about Stream and to learn to type similar code?

Use System.out.println(s); to see why.

I like it!

I thought the same. I thought it will be test case number per number 9, 1, 1,...

Not an issue.

You dont need to type anything in the test cases. Those are for testing. There are test cases written for when you submit it.

I ocmpleted this challenge with no effort, using Java. So I know it's not broken.

Thanks from me too!
But in Eclipse it looks ugly :(

I have problem too doing in Java. I thought i made mistake in my code and i unlocked solution. Then i copy/paste several solutions too see how i have to do but i get error massage again.
What do i have to type in "Your Test Cases:"? I entered:
1
3
6
12

Hi,
Are there any way how can i configure this dark color sheme for Eclipse? I really like it on first look.