public class SingleSales {

public static void main(String[] args) {

doStuff(new Pen(10.00));

doStuff(new Book(250.00, 5.00));

}

public static void doStuff(Sellable item) {

double income = item.sell();

System.out.println("Income: $" + income);

}

}

interface Sellable {

double sell();

}

class Book implements Sellable {

private double price;

private double discount;

public Book(double price, double discount) {

this.price = price;

this.discount = discount;

}

@Override

public double sell() {

return price - (price * discount / 100.00);

}

}

class Pen implements Sellable {

private double price;

public Pen(double price) {

this.price = price;

}

@Override

public double sell() {

return price;

}

}