There's an order of precedence of operators in
Java (and most other languages). Operators with higher precedence get applied first regardless of the order they appear - unless you use brackets to force a particular order.
For a possibly more familiar example, what would you expect
(1 + 2*3) to be? The * has higher precedence than +, so it's 7, not 9.
Another example: = is actually an operator. If it wasn't for the rules of precedence, something as straightforward as
x = a + 1 really wouldn't do what you'd expect (think about what the effect is if you applied that left-to-right).
See
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html for the full rules of precedence.
As a rule, though, when writing code if you have any confusion as to what the order will be, add brackets to make it clearer, even if they aren't strictly needed.