Why don't you experiment with the code yourself and see what happens? Add parentheses, and see what happens. For example:
This prints 12 instead of 15. And this:
Just try it out and discover for yourself what happens exactly. By playing with it and finding it out yourself, you learn more then when somebody else gives you the answer directly.
p.s. Please, never write code like this in a real application. It's fine as a brain teaser, to learn how operators work in Java, but in a real application this will only confuse programmers who need to maintain the code.