Java Reference
In-Depth Information
prints the value of
println
's conditional-expression argument. The conditional expres-
sion in this statement evaluates to the string
"Passed"
if the
boolean
expression
student-
Grade
>=
60
is true and to the string
"Failed"
if it's false. Thus, this statement with the
conditional operator performs essentially the same function as the
if
…
else
statement
shown earlier in this section. The precedence of the conditional operator is low, so the en-
tire conditional expression is normally placed in parentheses. We'll see that conditional ex-
pressions can be used in some situations where
if
…
else
statements cannot.
Error-Prevention Tip 4.2
Use expressions of the same type for the second and third operands of the
?:
operator to
avoid subtle errors.
The example of Figs. 4.4-4.5 demonstrates a nested
if
…
else
statement that determines
a student's letter grade based on the student's average in a course.
Class
Student
Class
Student
(Fig. 4.4) has features similar to those of class
Account
(discussed in
Chapter 3). Class
Student
stores a student's name and average and provides methods for
manipulating these values. The class contains:
•i st e i le
name
of type
String
(line 5) to store a
Student
's name
•i st e i le
average
of type
double
(line 6) to store a
Student
's average in
a course
• a constructor (lines 9-18) that initializes the
name
and
average
—in Section 5.9,
you'll learn how to express lines 15-16 and 37-38 more concisely with logical
operators that can test multiple conditions
•m t s
setName
and
getName
(lines 21-30) to
set
and
get
the
Student
's
name
•m t s
setAverage
and
getAverage
(lines 33-46) to
set
and
get
the
Student
's
average
•m t d
getLetterGrade
(lines 49-65), which uses
nested
if
…
else
statements
to
determine the
Student
's
letter grade
based on the
Student
's
average
The constructor and method
setAverage
each use
nested
if
statements
(lines 15-17
and 37-39) to
validate
the value used to set the
average
—these statements ensure that the
value is greater than
0.0
and
less than or equal to
100.0
; otherwise,
average
's value is left
unchanged
. Each
if
statement contains a
simple
condition. If the condition in line 15 is
true
,
only then will the condition in line 16 be tested, and
only
if the conditions in both line 15
and
line 16 are
true
will the statement in line 17 execute.
Software Engineering Observation 4.1
Recall from Chapter 3 that you should not call methods from constructors (we'll explain why
in Chapter 10, Object-Oriented Programming: Polymorphism and Interfaces). For this
reason, there is duplicated validation code in lines 15-17 and 37-39 of Fig. 4.4 and in
subsequent examples.
