How did it I get this answer?

Question

I have following java code:

public class myClass {

    public static void main(String[] args) {

        System.out.println("Hello World!");

        int x = 20;
        int y = 10;

        double z = x++ - y * 7 / --y + x * 10;
        System.out.println(z);
    }
}

I got 223.0 output. But I would like to know the step by step process. Someone please explain it according to operator precedence.

For educational purposes, try writing out your arithmetic expression using nested parentheses, according to the order of operations rules in Java. — Tim Biegeleisen, Nov 19 '18 at 05:29
Terrible title. Edit to describe your particular technical issue. — Basil Bourque, Nov 19 '18 at 05:51
Possible duplicate of [Operator precedence in Java](https://stackoverflow.com/questions/8112221/operator-precedence-in-java) — Intsab Haider, Nov 19 '18 at 05:51

Robby Cornelissen · Answer 1 · 2018-11-19T05:58:21.247

I decided to write up an answer because there's a gotcha in there that is unrelated to operator precedence (see step 3).

Step 0: The input expression—

   x++ - y * 7 / --y + x * 10;

Step 1: In terms of operator precedence, increment/decrement have a higher precedence than multiplication/division, and multiplication/division have a higher precedence than addition/subtraction, so add some parentheses to clarify that—

   (x++) - (y * 7 / (--y)) + (x * 10);

Step 2: The next thing to do is to replace the variables with values, taking into account how the pre/post-increment/decrement operators work—

   20 - (10 * 7 / 9) + (21 * 10)
//  ^             ^      ^
//  |           Pre-1    |
//  |                    |
//  + -----------------Post+1

Step 3: The only thing not related to operator precedence: performing an operation on integer operands yields an integer result, even if the result of the expression is assigned to a floating point type. Therefore, 10 * 7 / 9 yields 7—

   20 - (7) + (210)

Step 4: Expressions are evaluated from left to right—

   20 - 7 + 210
   13 + 210
   223

Step 5: The integer result is assigned to a double—

   223.0

How did it I get this answer?

1 Answers1