Hands on Testing Java: Lab #3

Experiment #7: Operator Associativity

Precedence Is Half the Story

So precedence (seen in the previous experiment) determines the order of evaluation in many cases, but what happens when operators with the same precedence are next? Who goes first?

Consider this expression:

8 - 4 - 2

If the leftmost subtraction is performed first, then the expression evaluates as follows:

(8 - 4) - 2 = 4 - 2 = 2

But if the rightmost subtraction is performed first, then the expression evaluates like so:

8 - (4 - 2) = 8 - 2 = 6

Give it guess, as before.

assertEquals("8 minus 4 minus 2", ???, 8 - 4 - 2);

Operator Associativity

Once again the order in which operators are applied determines the value of the expression. However, some characteristic other than precedence must be used in a situation like this because each of the operators in question have the same precedence level.

This new characteristic is called operator associativity. Associativity describes how the compiler should parenthesize an expression when precedence has been exhausted. There are two options:

1. A left associative operator parenthesizes from the left:

   (8 - 4) - 2
   

2. A right associative operators parenthesize from the right:

   8 - (4 - 2)
   

While Java has both left and right associative operators, all arithmetic and logic operators have the same associativity.

Terminology

left associative, operator associativity, right associative