# CS 521 Homework 6

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## 7.1 (The Rectangle class)

Following the example of the Circle class in Section
7.2, design a class named Rectangle to represent a rectangle. The class
contains:

■ Two data fields named width and height.
■ A constructor that creates a rectangle with the specified width and
height.
The default values are 1 and 2 for the width and height, respectively.
■ A method named getArea() that returns the area of this rectangle.
■ A method named getPerimeter() that returns the perimeter.

Draw the UML diagram for the class, and then implement the class.
Write a test
program that creates two Rectangle objects—one with width 4 and
height 40
and the other with width 3.5 and height 35.7. Display the width, height,
area,
and perimeter of each rectangle in this order.

## 7.3 (The Account class)

Design a class named Account that contains:
■ A private int data field named id for the account.
■ A private float data field named balance for the account.
■ A private float data field named annualInterestRate that stores the
current
interest rate.

■ A constructor that creates an account with the specified id (default 0),
initial
balance (default 100), and annual interest rate (default 0).
■ The accessor and mutator methods for id, balance, and
annualInterestRate.
■ A method named getMonthlyInterestRate() that returns the monthly
interest rate.
■ A method named getMonthlyInterest() that returns the monthly
interest.
■ A method named withdraw that withdraws a specified amount from
the
account.
■ A method named deposit that deposits a specified amount to the
account.

Draw the UML diagram for the class, and then implement the class.
(Hint: The
method getMonthlyInterest() is to return the monthly interest amount,
not
the interest rate. Use this formula to calculate the monthly interest:
balance *
monthlyInterestRate. monthlyInterestRate is annualInterestRate
/ 12. Note that annualInterestRate is a percent (like 4.5%). You need to
divide it by 100.)

Write a test program that creates an Account object with an account id of
1122, a
balance of \$20,000, and an annual interest rate of 4.5%. Use the
withdraw
method to withdraw \$2,500, use the deposit method to deposit \$3,000,
and print
the id, balance, monthly interest rate, and monthly interest.
*7.5 (Geometry: n-sided regular polygon)
An n-sided regular polygon’s sides all have
the same length and all of its angles have the same degree (i.e., the
polygon is
both equilateral and equiangular). Design a class named RegularPolygon
that
contains:
■ A private int data field named n that defines the number of sides in the
polygon.
■ A private float data field named side that stores the length of the side.
■ A private float data field named x that defines the x-coordinate of the
center of
the polygon with default value 0.
■ A private float data field named y that defines the y-coordinate of the
center of
the polygon with default value 0.
■ A constructor that creates a regular polygon with the specified n
(default 3),
side (default 1), x (default 0), and y (default 0).
■ The accessor and mutator methods for all data fields.
■ The method getPerimeter() that returns the perimeter of the polygon.
■ The method getArea() that returns the area of the polygon. The
formula for
computing the area of a regular polygon is
Draw the UML diagram for the class, and then implement the class.

Write a test program
that creates three RegularPolygon objects, created using
RegularPolygon(),
using RegularPolygon(6, 4) and RegularPolygon(10, 4, 5.6, 7.8). For
each object, display its perimeter and area.
*7.7 (Algebra: linear equations)

Design a class named LinearEquation for a
system of linear equations:
The class contains:
■ The private data fields a, b, c, d, e, and f with get methods.
■ A constructor with the arguments for a, b, c, d, e, and f.
■ Six get methods for a, b, c, d, e, and f.
■ A method named isSolvable() that returns true if is not 0.
■ The methods getX() and getY() that return the solution for the
equation.

Draw the UML diagram for the class, and then implement the class.
Write a test
program that prompts the user to enter a, b, c, d, e, and f and displays the
result.
If is 0, report that “The equation has no solution.” See Exercise 4.3 for
sample runs.

## 12.1 (The Triangle class)

Design a class named Triangle that extends the
GeometricObject class. The Triangle class contains:
■ Three float data fields named side1, side2, and side3 to denote the
three
sides of the triangle.
■ A constructor that creates a triangle with the specified side1, side2,
and
side3 with default values 1.0.
■ The accessor methods for all three data fields.
■ A method named getArea() that returns the area of this triangle.
■ A method named getPerimeter() that returns the perimeter of this
triangle.
■ A method named __str__() that returns a string description for the
triangle.
For the formula to compute the area of a triangle, see Exercise 2.14. The
__str__() method is implemented as follows:
return “Triangle: side1 = ” + str(side1) + ” side2 = ” +
str(side2) + ” side3 = ” + str(side3)

Draw the UML diagrams for the classes Triangle and GeometricObject.
Implement the Triangle class. Write a test program that prompts the user
to
enter the three sides of the triangle, a color, and 1 or 0 to indicate
whether the triangle
is filled. The program should create a Triangle object with these sides
and
set the color and filled properties using the input. The program should
display the
triangle’s area, perimeter, color, and True or False to indicate whether
the triangle
is filled or not.

## **12.3 (Game: ATM machine)

Use the Account class created in Exercise 7.3 to simulate
an ATM machine. Create ten accounts in a list with the ids 0, 1, …, 9,
and an initial
balance of \$100. The system prompts the user to enter an id. If the id is
entered
incorrectly, ask the user to enter a correct id. Once an id is accepted, the
main
menu is displayed as shown in the sample run. You can enter a choice of
1 for
viewing the current balance, 2 for withdrawing money, 3 for depositing
money,
and 4 for exiting the main menu. Once you exit, the system will prompt
for an id
again. So, once the system starts, it won’t stop.