Question

This exercise guides you through the process of converting an Area and Perimeter application from a procedural application to an object-oriented application.
Create and use an object
1. Open the project named ch04_ex2_Area and Perimeter that’s stored in the ex_starts folder. Then, review the code for the Main class.
2. Create a class named Rectangle and store it in the murach.rectangle package.
3. In the Rectangle class, add instance variables for length and width. The, code the get and set methods for these instance variables. If possible, use your IDE to generate the get and set methods. With NetBeans, you can get started by selecting the RefactorEncapsulate Fields command.
4. Add a zero-argument constructor that initializes the length and width to 0.
5. Add a get method that calculates the area of the rectangle and returns a double value for the result. If you want, you can copy the code that performs this calculation from the Main class.
6. Add a get method that returns the area as a String object with standard numeric formatting and a minimum of three decimal places. To make it easy to refer to the NumberFormat class, you should add an import statement for it.
7. Repeat the previous two steps for the perimeter.
8. Open the Main class. Then, add code that creates a Rectangle object and sets its length and width.
9. Modify the code that displays the calculations so it uses the methods of the Rectangle object to get the area and perimeter of the rectangle.
10. Remove any leftover code from the Main class that’s unnecessary including any unnecessary import statements.
11. Run the application and test it with valid data. It should calculate the area and perimeter for a rectangle.
Overload the constructor
12. Open the Rectanble class. Then, overload the constructor by supplying a second constructor that accepts two arguments: length and width. This constructor should set the length and width of the rectangle to the values supplied by these arguments.
13. Open the Main class. Then, modify its code so it uses this constructor instead of the zero-argument constructor.
14. Run the application and test it to make sure it still works correctly.

----------------------

package murach.rectangle;

import java.text.NumberFormat;
import java.util.Scanner;

public class Main {

public static void main(String args[]) {
System.out.println("Welcome to the Area and Perimeter Calculator");
System.out.println();

Scanner sc = new Scanner(System.in);
String choice = "y";
while (choice.equalsIgnoreCase("y")) {
// get input from user
System.out.print("Enter length: ");
double length = Double.parseDouble(sc.nextLine());

System.out.print("Enter width: ");
double width = Double.parseDouble(sc.nextLine());

// calculate total
double area = width * length;
double perimeter = 2 * width + 2 * length;
  
// format and display output
NumberFormat number = NumberFormat.getNumberInstance();
number.setMinimumFractionDigits(3);
String message =
"Area: " + number.format(area) + "\n" +
"Perimeter: " + number.format(perimeter) + "\n";
System.out.println(message);

// see if the user wants to continue
System.out.print("Continue? (y/n): ");
choice = sc.nextLine();
System.out.println();
}
System.out.println("Bye!");
}
}

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

// Rectangle.java

package murach.rectangle;

import java.text.NumberFormat;

public class Rectangle {

              // attributes

              private double length;

              private double width;

              // default constructor, sets length and width to 0

              public Rectangle() {

                           length = 0;

                           width = 0;

              }

              // constructor taking arguments to initialize length and width

              public Rectangle(double length, double width) {

                           this.length = length;

                           this.width = width;

              }

              // getters and setters

              public double getLength() {

                           return length;

              }

              public void setLength(double length) {

                           this.length = length;

              }

              public double getWidth() {

                           return width;

              }

              public void setWidth(double width) {

                           this.width = width;

              }

              // method to calculate the area of rectangle

              public double getArea() {

                           return length * width;

              }

              // returns the area of rectangle as a labeled and formatted String

              public String getAreaString() {

                           NumberFormat number = NumberFormat.getNumberInstance();

                           number.setMinimumFractionDigits(3);

                           String str = "Area: " + number.format(getArea());

                           return str;

              }

             

              // method to calculate the perimeter of rectangle

              public double getPerimeter() {

                           return 2 * (length + width);

              }

              // returns the perimeter of rectangle as a labeled and formatted String

              public String getPerimeterString() {

                           NumberFormat number = NumberFormat.getNumberInstance();

                           number.setMinimumFractionDigits(3);

                           String str = "Perimeter: " + number.format(getPerimeter());

                           return str;

              }

}

//Main.java (updated)

package murach.rectangle;

import java.util.Scanner;

public class Main {

              public static void main(String args[]) {

                           System.out.println("Welcome to the Area and Perimeter Calculator");

                           System.out.println();

                           Scanner sc = new Scanner(System.in);

                           //creating an object of Rectangle

                           Rectangle rectangle=null;

                           String choice = "y";

                           while (choice.equalsIgnoreCase("y")) {

                                         // get input from user

                                         System.out.print("Enter length: ");

                                         double length = Double.parseDouble(sc.nextLine());

                                         System.out.print("Enter width: ");

                                         double width = Double.parseDouble(sc.nextLine());

                                        

                                         //creating a rectangle with entered length and width

                                         rectangle=new Rectangle(length, width);

                                         //displaying area and perimeter strings

                                         System.out.println(rectangle.getAreaString());

                                         System.out.println(rectangle.getPerimeterString());

                                         // see if the user wants to continue

                                         System.out.print("Continue? (y/n): ");

                                         choice = sc.nextLine();

                                         System.out.println();

                           }

                           System.out.println("Bye!");

              }

}

/*OUTPUT*/

Welcome to the Area and Perimeter Calculator

Enter length: 25.5

Enter width: 12.8

Area: 326.400

Perimeter: 76.600

Continue? (y/n): y

Enter length: 220.55

Enter width: 123.456

Area: 27,228.221

Perimeter: 688.012

Continue? (y/n): n

Bye!