Java Reference
In-Depth Information
154
System.out.printf(
"%9.2f%n"
, average);
155
}
156
}
157
}
// end class GradeBook
Fig. 7.18
|
GradeBook
class using a two-dimensional array to store grades. (Part 4 of 4.)
Methods
getMinimum
and
getMaximum
Methods
getMinimum
,
getMaximum
,
outputBarChart
and
outputGrades
each loop
through array
grades
by using nested
for
statements—for example, the nested enhanced
for
statement (lines 50-59) from the declaration of method
getMinimum
. The outer en-
hanced
for
statement iterates through the two-dimensional array
grades
, assigning suc-
cessive rows to parameter
studentGrades
on successive iterations. The square brackets
following the parameter name indicate that
studentGrades
refers to a one-dimensional
int
array—namely, a row in array
grades
containing one student's grades. To find the
lowest overall grade, the inner
for
statement compares the elements of the current one-
dimensional array
studentGrades
to variable
lowGrade
. For example, on the first iteration
of the outer
for
, row 0 of
grades
is assigned to parameter
studentGrades
. The inner en-
hanced
for
statement then loops through
studentGrades
and compares each
grade
value
with
lowGrade
. If a grade is less than
lowGrade
,
lowGrade
is set to that grade. On the sec-
ond iteration of the outer enhanced
for
statement, row 1 of
grades
is assigned to
stu-
dentGrades
, and the elements of this row are compared with variable
lowGrade
. This
repeats until all rows of
grades
have been traversed. When execution of the nested state-
ment is complete,
lowGrade
contains the lowest grade in the two-dimensional array.
Method
getMaximum
works similarly to method
getMinimum
.
Method
outputBarChart
Method
outputBarChart
in Fig. 7.18 is nearly identical to the one in Fig. 7.14. However,
to output the overall grade distribution for a whole semester, the method here uses nested
enhanced
for
statements (lines 107-111) to create the one-dimensional array
frequency
based on all the grades in the two-dimensional array. The rest of the code in each of the
two
outputBarChart
methods that displays the chart is identical.
Method
outputGrades
Method
outputGrades
(lines 132-156) uses nested
for
statements to output values of the
array
grades
and each student's semester average. The output (Fig. 7.19) shows the result,
which resembles the tabular format of a professor's physical grade book. Lines 138-139
print the column headings for each test. We use a counter-controlled
for
statement here
so that we can identify each test with a number. Similarly, the
for
statement in lines 144-
155 first outputs a row label using a counter variable to identify each student (line 146).
Although array indices start at 0, lines 139 and 146 output
test + 1
and
student + 1
, re-
spectively, to produce test and student numbers starting at 1 (see the output in Fig. 7.19).
The inner
for
statement (lines 148-149) uses the outer
for
statement's counter variable
student
to loop through a specific row of array
grades
and output each student's test
grade. An enhanced
for
statement can be nested in a counter-controlled
for
statement,
and vice versa. Finally, line 153 obtains each student's semester average by passing the cur-
rent row of
grades
(i.e.,
grades[student]
) to method
getAverage
.
