Structured and readable code.

Now I understood, why author of this kata said "java is heaven".

I couldn't agree more

We can also modify global variable through IIB (Instance Initialization Blocks). You can check my solution for reference.

Learning is life long process and learning is frustrating for one who do not love his work. It totally depends on us what is it we love to do.

If I do coding for money, job, status, etc but do not love it then frustration is natural.

Neat solution author. I have one question. Why are returning an array from partition method? Instead you could have just return the integer j (index of pivot)

I like you approach

you have to make your code dynamic rather than hard code. By dynamic I mean felxiable with any input. then only you can pass all the cases.