1.2.3 Precedence of Operations

Since Java uses conventional infix notation for expressions it relies on the notion of precedence to determine how expressions like

12 * 5 + 10

should be interpreted. The Java operations given in the preceding subsection are divided into the following precedence groups:

prefix operators	- !
multiplicative	star / %
additive	+ -
relational	< > >= <=
equality	== !=
logical and	&&
logical or	||
conditional	? $\dots$ :

from highest to lowest. A higher precedence operator has greater ``binding power''. For example, the expression

72. - 32. * 1.8

is equivalent to

72. - (32. * 1.8)

because star has higher precedence than infix -.

Finger Exercise: In the DrJava Interactions window: available, try evaluating the following expressions:

72. - 32. * 1.8
(72. - 32.) * 1.8

All of infix operators listed above are left-associative: when infix operators of equal precedence are chained together, the leftmost operator has precedence. For example,

72. - 30. - 12.

is equivalent to

(72. - 30.) - 12.

Parentheses can be used to override the built-in precedence and associativity of operators. Hence,

(72. - 32.) * 1.8

equals 40*1.8. Similarly,

72. - (30. - 12.)

equals

72. - 18.

It is a good idea to use parentheses if you have any doubts about the precedence relationship between consecutive operators. The judicious use of parentheses makes complex expressions easier to read.

Finger Exercise: In the DrJava Interactions window, try evaluating the following expressions:

72. - 30. - 12.
72. - (30. - 12.)