In java you dont have to do that

Read the description!

This function will return undefined (NULL in PHP) if any of the values aren't numbers.

Which I assume is None in Python.

Anyone managed to complete this in Java? I am not sure how to return 'undefined' from function which return int.

Any tips for someone trying to solve that in Java 8?

Thanks for your feedback! ;-)
Java version was created by translator. I've checked the code and do some changes:

1. Add testcase information in the random tests

2. Change the random string generate function, such as "word  !!! word" will not appear in tests.

I've passed your kata just after few attemptions of running tests. When cases described above were not generated I succeed. I think that should be fixed or explained in kata description just to save others time for investigation.

Thanks for quick response. I'm using Java 8.
I can't preview test cases.
The only one I fail is:
testRandom(SolutionTest)
✘ String index out of range: -1

I run my code in eclipse to test all available test cases and cases from examples and my code do it correctly but I still can't pass that 'testRandom'.
edit1: ok, I've found that I can preview 'testRandom' being in discourse tab.
edit2: ok, my program fault at test case: '!! D31 !ddbDcE! CBcbBdeE3'. I didn't expected the word will contain only exclamation marks.
edit3: now I got single '!' from random: '!!CBd1cEAd3Ac2b1! e213242c EBB4! !'
edit4: sometimes it produces double spaces: '1Ed__!!3Ee!! 5A2baB32D1!!' (i marked it with double underscore here)

It's not a valid word.
It should not appear in the tests ;-)
Are you meet a single "!" in the testcase? If you saw it, please tell me which language you are using, thanks.

How to treat such case: " !" ? Should I remove '!' or leave it?

This Kata is a not worth effort and time. Even I print correct diamond I can't pass those test cases.