Rearranging code using classes?

Question

I'm currently working on a project that was assigned to me and I'm having a bit of trouble trying to find out how I should start. This assignment is to rewrite a program using classes instead of just putting everything into the main program. Here is my code that I created that has to rewritten:

public class Lab14 {
public static void main(String[] args)  {
int Numbook1=0;
int Numbook2=0;
int Numbook3=0;
double priceOfDesignPatterns=32.46;
double priceOfEffectiveJava=35.48;
double priceOfJavaPuzzlers=27.86;
String book1="Design Patterns";
String book2="Effective Java";
String book3="Java Puzzlers";
final double SALES_TAX=.065;
String choice;
int finished=0;


Scanner input=new Scanner(System.in);
System.out.println("Welcome to ECommerce!");
System.out.println("The books we have in stock are: ");
System.out.println(book1+", "+book2+", "+book3);
System.out.println("Please enter the name of the book you wish to purchase.  Press 'q' to quit.");

while (finished==0) 
{
choice=input.nextLine();
    if (choice.equals(book1))   
    {
        System.out.println("How many "+book1+"(s) do you wish to buy?");
        Numbook1=(input.nextInt())+Numbook1;
        System.out.println(Numbook1+" copies of "+book1+" are in your cart.");
        System.out.println("Enter the name of the next book you would like to purchase, or press 'q' to quit.");
    }
    else if (choice.equals(book2))
    {
        System.out.println("How many "+book2+"(s) do you wish to buy?");
        Numbook2=(input.nextInt())+Numbook2;
        System.out.println(Numbook2+" copies of "+book2+" are in your cart.");
        System.out.println("Enter the name of the next book you would like to purchase, or press 'q' to quit.");
    }
    if (choice.equals(book3))
    {
        System.out.println("How many "+book3+"(s) do you wish to buy?");
        Numbook3=(input.nextInt())+Numbook3;
        System.out.println(Numbook3+" copies of "+book3+" are in your cart.");
        System.out.println("Enter the name of the next book you would like to purchase, or press 'q' to quit.");
    }
    if (choice.equals("q"))
    {
        double total=0;
        double totalTax=0;

        total=(Numbook1*priceOfDesignPatterns)+(Numbook2*priceOfEffectiveJava)+(Numbook3*priceOfJavaPuzzlers);
        totalTax=total*SALES_TAX;
        System.out.println("Your cart contains: ");
        System.out.println(Numbook1+" "+book1+"(s), "+Numbook2+" "+book2+"(s), "+Numbook3+" "+book3+"(s).");
        System.out.println("Sales Tax: $"+totalTax);
        System.out.println("Your total cost is: $"+(totalTax+total));
        finished=1;
    }
}
}
}

Now I know that I have to write a couple of classes to construct book1,2,3 and also to set the price and access them later, but I'm just really lost on how to start the process and aggregate everything together. If someone could guide me in the right direction it would be greatly appreciated! Thank you so much.

Answer 1

I will try to guide you towards the solution. The construct of the code may be as follows:

class Book {

    String name;
    double price;

    Book(String name, double price) {
        this.name = name;
        this.price = price;
    }

    public double getPrice() {
        return this.price;
    }

    public String getName() {
        return this.name;
    }

}

You can use this Book class to define all your books. Write the set methods for this class yourself. You can use set-get methods over class variables for easy access and modifications. Next, you can have something like the following Cart class to keep track of all books user has chosen.

class Cart {

    ArrayList<Book> books;

    Cart() {
        books = new ArrayList<>();
    }

    public void addToCart(Book book) {
        books.add(book);
    }

    public ArrayList<Book> getCart() {
        return books;
    }

}

I will ask you to write a Cost class yourself in which you can compute the cost of all books added in the cart and add the sales tax to get the final cost.

You may then have a handler class like the one you have mentioned in your code to define books and generate cart for the user and compute the cost of the cart.

The objective of this assignment is to help you understand the basics of object oriented programming and modeling real world problems. I hope you get a hint of how it works.