The ABCs of Programming - Java 6 - page 48

The following example shows a comparison operator in use:
boolean hip;
int age = 36;
hip = age < 25;
The expression age < 25 produces a result of either true or false , depending on the
value of the integer age . Because age is 36 in this example (which is not less than 25),
hip is given the Boolean value false .
Logical Operators
Expressions that result in Boolean values, such as comparison operations, can be com-
bined to form more complex expressions. This is handled through logical operators,
which are used for the logical combinations AND , OR , XOR , and logical NOT .
For AND combinations, the & or && logical operators are used. When two Boolean expres-
sions are linked by the & or && operators, the combined expression returns a true value
only if both Boolean expressions are true.
Consider this example:
boolean extraLife = (score > 75000) & (playerLives < 10);
This expression combines two comparison expressions: score > 75000 and
playerLives < 10 . If both of these expressions are true, the value true is assigned to
the variable extraLife . In any other circumstance, the value false is assigned to the
variable.
The difference between “&” and “&&” lies in how much work Java does on the com-
bined expression. If “&” is used, the expressions on either side of the “ & ” are evaluated
no matter what. If “&&” is used and the left side of the “&&” is false, the expression on
the right side of the “&&” never is evaluated.
For OR combinations, the “|” or “||” logical operators are used. These combined expres-
sions return a true value if either Boolean expression is true.
Consider this example:
boolean extralife = (score > 75000) || (playerLevel == 0);
This expression combines two comparison expressions: score > 75000 and
playerLevel = 0 . If either of these expressions is true, the value true is assigned to the
variable extraLife . Only if both of these expressions are false will the value false be
assigned to extraLife .