Love it!

I'd say they're head and last.

why are h and l used as variable names? do they stand for something?

That's Java 11 or later

I am stunned. Very good solution.

Is checking for null or returning string smaller/equal 4 must have?
I did code like this and it has no error with empty string and properly showing 1-4 character strings

??

Excellent ! This solution worked with an unordered list. For example : [ 1, 5, 3, 9] return 7

You could use the string repeat function tocreatedthe masked part

here better to use StringBuilder.

+1 for readability 💀

put str.kength() in an integer variable for more neat code

You did it great!

TIL! I thought the .replaceAll() ment it replaced all occurences it finds, and .replace() only one.
Thanks!

could you elaborate why the replace method is better regarding the regex?

wtf