package shop;

public class Book extends Item
{
    private String title;
    
    public Book(String title, double purchasePrice, double salePrice)
    {
        this(title, 0, purchasePrice, salePrice);
    }
    
    public Book(String title, int numberPens, double purchasePrice, double salePrice)
    {
        super(numberPens, purchasePrice, salePrice);
        this.title = title;
    }
    
    public void printDetails()
    {
        System.out.printf("%-20s  ", title);
        super.printDetails();
    }
}


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

package shop;

public abstract class Item
{
    private int numberPurchased;
    private double purchasePrice;
    private double salePrice;
    private int numberSold;
    
    public Item(int numberPurchased, double purchasePrice, double salePrice)
    {
        this.numberPurchased = numberPurchased;
        this.purchasePrice = purchasePrice;
        this.salePrice = salePrice;
        numberSold = 0;
    }
    
    public void purchase(int numItems)
    {
        numberPurchased += numItems;
    }
    
    public void sell(int numItems)
    {
        numberSold += numItems;
    }
    
    public double calcProfit()
    {
        return numberSold * (salePrice - purchasePrice);
    }
    
    public void printDetails()
    {
        System.out.printf("%3d @ %6.2f  %3d @ %6.2f  %5.2f\n", 
                          numberPurchased, purchasePrice, numberSold, salePrice, calcProfit());
    }
}


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


package shop;

public class Pen extends Item
{
    private String inkColour;
    
    public Pen(String inkColour, double purchasePrice, double salePrice)
    {
        this(inkColour, 0, purchasePrice, salePrice);
    }
    
    public Pen(String inkColour, int numberPens, double purchasePrice, double salePrice)
    {
        super(numberPens, purchasePrice, salePrice);
        this.inkColour = inkColour;
    }
    
    public void printDetails()
    {
        System.out.printf("%-6s  ", inkColour);
        super.printDetails();
    }
}


----------


public class Shop
{
    public static void main(String args[])
    {
        Book book1, book2, book3;
        Pen pen1, pen2;
        
        //create the objects
        book1 = new Book("Pigs may fly", 100, 120);
        book2 = new Book("Pigs can't fly", 75, 100);
        book3 = new Book("Pigs must not fly", 10, 75, 100);
        
        pen1 = new Pen("Black", 10, 10, 15);
        pen2 = new Pen("Blue", 10, 15);
        
        //manipulate the objects
        book1.purchase(10);
        book2.purchase(10);
        pen2.purchase(10);
        
        book1.sell(5);
        book2.sell(2);
        book3.sell(1);
        
        pen1.sell(10);
        pen2.sell(3);
        
        //print a report
        System.out.println("\nBooks");
        System.out.printf("%-20s  %12s  %12s  %6s\n", 
                          "Title", "Bought", "Sold", "Profit");
        book1.printDetails();
        book2.printDetails();
        book3.printDetails();
        
        System.out.println("\nPens");
        System.out.printf("%-6s  %12s  %12s  %6s\n", 
                          "Ink", "Bought", "Sold", "Profit");
        pen1.printDetails();
        pen2.printDetails();
        
        System.out.print("\nTotal profit: ");
        double sum = book1.calcProfit();
        sum += book2.calcProfit();
        sum += book3.calcProfit();
        sum += pen1.calcProfit();
        sum += pen2.calcProfit();
        System.out.println(sum + "p");
    }
}