Java Reference
In-Depth Information
This
if
statement contains two simple conditions. The condition
gender == FEMALE
com-
pares variable
gender
to the constant
FEMALE
to determine whether a person is female. The
condition
age
>=
65
might be evaluated to determine whether a person is a senior citizen.
The
if
statement considers the combined condition
gender ==
FEMALE
&& age >=
65
which is true if and only if
both
simple conditions are true. In this case, the
if
statement's
body increments
seniorFemales
by
1
. If either or both of the simple conditions are false,
the program skips the increment. Some programmers find that the preceding combined
condition is more readable when
redundant
parentheses are added, as in:
(gender ==
FEMALE
) && (age >=
65
)
The table in Fig. 5.15 summarizes the
&&
operator. The table shows all four possible
combinations of
false
and
true
values for
expression1
and
expression2
. Such tables are
called
truth tables
. Java evaluates to
false
or
true
all expressions that include relational
operators, equality operators or logical operators.
expression1
expression2
expression1
&&
expression2
false
false
false
false
true
false
true
false
false
true
true
true
Fig. 5.15
|
&&
(conditional AND) operator truth table.
Conditional OR (
||
) Operator
Now suppose we wish to ensure that
either or both
of two conditions are true before we
choose a certain path of execution. In this case, we use the
||
(
conditional OR
) operator,
as in the following program segment:
if
((semesterAverage >=
90
) || (finalExam >=
90
))
System.out.println (
"Student grade is A"
);
This statement also contains two simple conditions. The condition
semesterAverage
>=
90
evaluates to determine whether the student deserves an A in the course because of a sol-
id performance throughout the semester. The condition
finalExam
>=
90
evaluates to de-
termine whether the student deserves an A in the course because of an outstanding
performance on the final exam. The
if
statement then considers the combined condition
(semesterAverage >=
90
) || (finalExam >=
90
)
and awards the student an A if
either or both
of the simple conditions are true. The only
time the message
"Student
grade
is
A"
is
not
printed is when
both
of the simple condi-
tions are
false
. Figure 5.16 is a truth table for operator conditional OR (
||
). Operator
&&
has a higher precedence than operator
||
. Both operators associate from left to right.
