Parentheses override the default precedence. Whatever is inside () gets evaluated first, regardless of operator priority.
System.out.println(3 + 4 * 2); // 11 (multiplication first)
System.out.println((3 + 4) * 2); // 14 (addition first)
Even when precedence would give you the correct result without parentheses, adding them makes your intent obvious. Compare these two:
boolean ok = a > 5 && b < 10; // works, but you have to know precedence
boolean ok = (a > 5) && (b < 10); // same result, immediately clear
When you're unsure about precedence, add parentheses. There is no runtime cost, and it prevents subtle bugs that come from misremembering the operator order.