Java Reference
In-Depth Information
Exercises
8.2
(Based on Section 8.14)
Explain the notion of package access in Java. Explain the negative
aspects of package access.
8.3
What happens when a return type, even
void
, is specified for a constructor?
8.4
(Rectangle Class)
Create a class
Rectangle
with attributes
length
and
width
, each of which
defaults to 1. Provide methods that calculate the rectangle's perimeter and area. It has
set
and
get
methods for both
length
and
width
. The
set
methods should verify that
length
and
width
are each
floating-point numbers larger than 0.0 and less than 20.0. Write a program to test class
Rectangle
.
8.5
(Modifying the Internal Data Representation of a Class)
It would be perfectly reasonable
for the
Time2
class of Fig. 8.5 to represent the time internally as the number of seconds since mid-
night rather than the three integer values
hour
,
minute
and
second
. Clients could use the same
pub-
lic
methods and get the same results. Modify the
Time2
class of Fig. 8.5 to implement the time as
the number of seconds since midnight and show that no change is visible to the clients of the class.
8.6
(Savings Account Class)
Create class
SavingsAccount
. Use a
static
variable
annualInter-
estRate
to store the annual interest rate for all account holders. Each object of the class contains a
private
instance variable
savingsBalance
indicating the amount the saver currently has on deposit.
Provide method
calculateMonthlyInterest
to calculate the monthly interest by multiplying the
savingsBalance
by
annualInterestRate
divided by 12—this interest should be added to
savings-
Balance
. Provide a
static
method
modifyInterestRate
that sets the
annualInterestRate
to a new
value. Write a program to test class
SavingsAccount
. Instantiate two
savingsAccount
objects,
saver1
and
saver2
, with balances of $2000.00 and $3000.00, respectively. Set
annualInterestRate
to 4%, then calculate the monthly interest for each of 12 months and print the new balances for
both savers. Next, set the
annualInterestRate
to 5%, calculate the next month's interest and print
the new balances for both savers.
8.7
(Enhancing Class
Time2
)
Modify class
Time2
of Fig. 8.5 to include a
tick
method that in-
crements the time stored in a
Time2
object by one second. Provide method
incrementMinute
to in-
crement the minute by one and method
incrementHour
to increment the hour by one. Write a
program that tests the
tick
method, the
incrementMinute
method and the
incrementHour
method
to ensure that they work correctly. Be sure to test the following cases:
a) incrementing into the next minute,
b) incrementing into the next hour and
c) incrementing into the next day (i.e., 11:59:59 PM to 12:00:00 AM).
8.8
(Enhancing Class
Date
)
Modify class
Date
of Fig. 8.7 to perform error checking on the ini-
tializer values for instance variables
month
,
day
and
year
(currently it validates only the month and
day). Provide a method
nextDay
to increment the day by one. Write a program that tests method
nextDay
in a loop that prints the date during each iteration to illustrate that the method works cor-
rectly. Test the following cases:
a) incrementing into the next month and
b) incrementing into the next year.
8.9
Rewrite the code in Fig. 8.14 to use a separate
import
declaration for each
static
member
of class
Math
that's used in the example.
8.10
Write an
enum
type
TrafficLight
, whose constants (
RED
,
GREEN
,
YELLOW
) take one parame-
ter—the duration of the light. Write a program to test the
TrafficLight
enum
so that it displays the
enum
constants and their durations.
8.11
(Complex Numbers)
Create a class called
Complex
for performing arithmetic with complex
numbers. Complex numbers have the form
realPart
+
imaginaryPart
*
i
