What is the right precedence of the math expression

Question

What is the correct sequence of the math operations in this expression in Java:

    a + b  * c / ( d - e )
1.    4    1   3     2
2.    4    2   3     1

I understand that result is the same in both answers. But I would like to fully understand the java compiler logic. What is executed first in this example - multiplication or the expression in parentheses? A link to the documentation that covers that would be helpful.

UPDATE: Thank you guys for the answers. Most of you write that the expression in parentheses is evaluated first. After looking at the references provided by Grodriguez I created little tests:

int i = 2;
System.out.println(i * (i=3)); // prints '6'
int j = 2;
System.out.println((j=3) * j); // prints '9'

Could anybody explain why these tests produce different results? If the expression in parentheses is evaluated the first I would expect the same result - 9.

Answer 1

Almost everybody so far has confused order of evaluation with operator precedence. In Java the precedence rules make the expression equivalent to the following:

a + (b  * c) / ( d - e )

because * and / have equal precedence and are left associative.

The order of evaluation is strictly defined as left hand operand first, then right, then operation (except for || and &&). So the order of evaluation is:

  a
      b
      c
    *
      d
      e
    -
  /
+

order of evaluation goes down the page. Indentation reflects the structure of the syntax tree

Edit

In response to Grodriguez's comments. The following program:

public class Precedence 
{
    private static int a()
    {
        System.out.println("a");
        return 1;
    }   
    private static int b()
    {
        System.out.println("b");
        return 2;
    }
    private static int c()
    {
        System.out.println("c");
        return 3;
    }
    private static int d()
    {
        System.out.println("d");
        return 4;
    }
    private static int e()
    {
        System.out.println("e");
        return 5;
    }

    public static void main(String[] args) 
    {
        int x = a() + b() * c() / (d() - e());
        System.out.println(x);
    } 
}

Produces the output

a
b
c
d
e
-5

which clearly shows the multiplication is performed before the subtraction.

Answer 2

As JeremyP has nicely shown us, the first answer is correct.

In general, the following rules apply:

• Every operand of an operator is evaluated before the operation itself is performed (except for ||, &&, and ? :)
• Operands are evaluated left to right. The left-hand operand of a binary operator appears to be fully evaluated before any part of the right-hand operand is evaluated.
• The order of evaluation respects parentheses and operator precedence:
  • Parentheses are evaluated first.
  • Operators are evaluated in order of precedence.
  • Operators with equal precedence are evaluated left-to-right, except for assignment operators which are evaluated right-to-left.

Note that the first two rules explain the result in your second question:

int i = 2;
System.out.println(i * (i=3)); // prints '6'
int j = 2;
System.out.println((j=3) * j); // prints '9'

Reference documentation:

http://java.sun.com/docs/books/jls/second_edition/html/expressions.doc.html#4779

Tutorial:

http://download.oracle.com/javase/tutorial/java/nutsandbolts/operators.html