# 5
This has been a fun problem to think about. I've had a great time tonight.
What I'm going to post will be over your head, but it illustrates what I mean when I advise you to think about the objects first.
I've written a little RentalAgency application that runs on the command line. It lets me associate a Customer with a Vehicle in a Contract object, which contains the start and end dates of the agreement.
The interesting bit comes in the PricingStrategy interface. Your rules for a discount on certain days made me think about how someone might write this in a such a way that they could easily change the business rules without having to rewrite the code.
I can change the pricing rules at will just by implementing a new class. I've included four examples for you to think about.
Notice how simple the object model is. I think it matches my understanding of how this might work pretty well. It's thirteen classes and interfaces, but not difficult to understand once you have it all in one spot.
See what you think. Thanks again for a fun problem. - %
Name.java
package rental;
import java.io.Serializable;
/**
* Encapsulation of a Name
* Date: Jan 27, 2007
* Time: 6:40:30 PM
*/
public class Name implements Serializable
{
private String first;
private String last;
public Name(String first, String last)
{
this.first = first;
this.last = last;
}
public String getFirst()
{
return first;
}
public String getLast()
{
return last;
}
public boolean equals(Object o)
{
if (this == o)
{
return true;
}
if (o == null || getClass() != o.getClass())
{
return false;
}
Name name = (Name) o;
if (first != null ? !first.equals(name.first) : name.first != null)
{
return false;
}
if (last != null ? !last.equals(name.last) : name.last != null)
{
return false;
}
return true;
}
public int hashCode()
{
int result;
result = (first != null ? first.hashCode() : 0);
result = 31 * result + (last != null ? last.hashCode() : 0);
return result;
}
public String toString()
{
return new StringBuilder().append("Name{").append("first='").append(first).append('\'').append(", last='").append(last).append('\'').append('}').toString();
}
}
VinFactory.java
package rental;
import java.util.Random;
/**
* Encapsulates the rules for generating a VIN
* Date: Jan 27, 2007
* Time: 6:48:23 PM
* @link http://en.wikipedia.org/wiki/Vehicle_identification_number
*/
public class VinFactory
{
private static final char [] LEGAL_CHARS =
{
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z',
};
private static final int DEFAULT_LENGTH = 17;
private static final String DEFAULT_MANUFACTURER = "JT"; // Only renting Toyotas
private static Random random = new Random();
/**
* Generate a 17-digit code for VIN
* @return VIN
*/
public static String getVin()
{
return getVin(DEFAULT_MANUFACTURER);
}
public static String getVin(String manufacturer)
{
StringBuilder vin = new StringBuilder(DEFAULT_LENGTH);
vin.append(manufacturer);
vin.append(getRandomString(DEFAULT_LENGTH-manufacturer.length()));
return vin.toString();
}
private static String getRandomString(int length)
{
StringBuilder builder = new StringBuilder(length);
for (int i = 0; i < length; ++i)
{
builder.append(LEGAL_CHARS[random.nextInt(LEGAL_CHARS.length)]);
}
return builder.toString();
}
}
Address.java
package rental;
import java.io.Serializable;
/**
* Classic Address
* Date: Jan 27, 2007
* Time: 6:41:50 PM
*/
public class Address implements Serializable
{
public static final String DEFAULT_STREET1 = "123 Main Street";
public static final String DEFAULT_STREET2 = "Apartment 4F";
public static final String DEFAULT_CITY = "Anytown";
public static final String DEFAULT_STATE = "NY";
public static final String DEFAULT_ZIP = "01010";
private Long id;
private String street1;
private String street2;
private String city;
private String state;
private String zip;
public Address()
{
this(DEFAULT_STREET1, DEFAULT_STREET2, DEFAULT_CITY, DEFAULT_STATE, DEFAULT_ZIP);//To change body of created methods use File | Settings | File Templates.
}
public Address(String street1, String street2, String city, String state, String zip)
{
this(null, street1, street2, city, state, zip);
}
public Address(Long id, String street1, String street2, String city, String state, String zip)
{
this.id = id;
this.street1 = street1;
this.street2 = street2;
this.city = city;
this.state = state;
this.zip = zip;
}
public Long getId()
{
return id;
}
public String getStreet1()
{
return street1;
}
public String getStreet2()
{
return street2;
}
public String getCity()
{
return city;
}
public String getState()
{
return state;
}
public String getZip()
{
return zip;
}
public boolean equals(Object o)
{
if (this == o)
{
return true;
}
if (o == null || getClass() != o.getClass())
{
return false;
}
Address address = (Address) o;
if (id != null ? !id.equals(address.id) : address.id != null)
{
return false;
}
return true;
}
public int hashCode()
{
return (id != null ? id.hashCode() : 0);
}
public String toString()
{
return new StringBuilder().append("Address{").append("id=").append(id).append(", street1='").append(street1).append('\'').append(", street2='").append(street2).append('\'').append(", city='").append(city).append('\'').append(", state='").append(state).append('\'').append(", zip='").append(zip).append('\'').append('}').toString();
}
}
Customer.java
package rental;
import java.io.Serializable;
/**
* Customer for rental system
* Date: Jan 27, 2007
* Time: 6:39:54 PM
*/
public class Customer implements Serializable
{
private Long id;
private Name name;
private Address address;
public Customer(Name name, Address address)
{
this(null, name, address);
}
public Customer(Long id, Name name, Address address)
{
this.id = id;
this.name = name;
this.address = address;
}
public boolean equals(Object o)
{
if (this == o)
{
return true;
}
if (o == null || getClass() != o.getClass())
{
return false;
}
Customer customer = (Customer) o;
if (id != null ? !id.equals(customer.id) : customer.id != null)
{
return false;
}
return true;
}
public int hashCode()
{
return (id != null ? id.hashCode() : 0);
}
public String toString()
{
String newline = System.getProperty("line.separator");
return new StringBuilder().append("Customer{").append("id=").append(id).append(newline).append(name).append(newline).append(address).append('}').toString();
}
}
Vehicle.java
package rental;
import java.io.Serializable;
/**
* Vehicle for rental system
* Date: Jan 27, 2007
* Time: 6:37:28 PM
*/
public class Vehicle implements Serializable
{
private Long id;
private String vin;
private String make;
private String model;
private int year;
public Vehicle(String make, String model, int year)
{
this(null, VinFactory.getVin(), make, model, year);
}
public Vehicle(Long id, String vin, String make, String model, int year)
{
this.id = id;
this.vin = vin;
this.make = make;
this.model = model;
this.year = year;
}
public Long getId()
{
return id;
}
public String getVin()
{
return vin;
}
public String getMake()
{
return make;
}
public String getModel()
{
return model;
}
public int getYear()
{
return year;
}
public boolean equals(Object o)
{
if (this == o)
{
return true;
}
if (o == null || getClass() != o.getClass())
{
return false;
}
Vehicle vehicle = (Vehicle) o;
if (id != null ? !id.equals(vehicle.id) : vehicle.id != null)
{
return false;
}
return true;
}
public int hashCode()
{
return (id != null ? id.hashCode() : 0);
}
public String toString()
{
return new StringBuilder().append("Vehicle{").append("id=").append(id).append(", vin='").append(vin).append('\'').append(", make='").append(make).append('\'').append(", model='").append(model).append('\'').append(", year=").append(year).append('}').toString();
}
}
Contract.java
package rental;
import java.io.Serializable;
import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
/**
* Contract for our rental system
* Date: Jan 27, 2007
* Time: 7:22:09 PM
*/
public class Contract implements Serializable
{
public static final DateFormat DEFAULT_DATE_FORMAT = new SimpleDateFormat("EEE dd-MMM-yyyy");
private Long id;
private Customer customer;
private Vehicle vehicle;
private Date begDate;
private Date endDate;
public Contract(Customer customer, Vehicle vehicle, Date begDate, Date endDate)
{
this(null, customer, vehicle, begDate, endDate);
}
public Contract(Long id, Customer customer, Vehicle vehicle, Date begDate, Date endDate)
{
if (endDate.before(begDate))
throw new IllegalArgumentException("end date must follow beg date");
this.id = id;
this.customer = customer;
this.vehicle = vehicle;
this.begDate = new Date(begDate.getTime());
this.endDate = new Date(endDate.getTime());
}
public Long getId()
{
return id;
}
public Customer getCustomer()
{
return customer;
}
public Vehicle getVehicle()
{
return vehicle;
}
public Date getBegDate()
{
return begDate;
}
public Date getEndDate()
{
return endDate;
}
public double getPrice(PricingStrategy pricingStrategy)
{
return pricingStrategy.calculatePrice(this);
}
public boolean equals(Object o)
{
if (this == o)
{
return true;
}
if (o == null || getClass() != o.getClass())
{
return false;
}
Contract contract = (Contract) o;
if (id != null ? !id.equals(contract.id) : contract.id != null)
{
return false;
}
return true;
}
public int hashCode()
{
return (id != null ? id.hashCode() : 0);
}
public String toString()
{
String newline = System.getProperty("line.separator");
return new StringBuilder().append("Contract{").append("id=").append(id).append(newline).append(customer).append(newline).append(vehicle).append(newline).append("begDate=").append(begDate).append(newline).append("endDate=").append(endDate).append('}').toString();
}
}
PricingStrategy.java
package rental;
/**
* Interface for generating pricing policies
* Date: Jan 27, 2007
* Time: 7:23:31 PM
*/
public interface PricingStrategy
{
double calculatePrice(Contract contract);
int getNumberOfDays(Contract contract);
}
AbstractPricingStrategy.java
package rental;
import java.util.Calendar;
/**
* Abstract class that all pricing strategies extend
* Date: Jan 27, 2007
* Time: 8:32:29 PM
*/
public abstract class AbstractPricingStrategy implements PricingStrategy
{
public int getNumberOfDays(Contract contract)
{
int numberOfDays = 0;
Calendar calendar = Calendar.getInstance();
calendar.setTime(contract.getBegDate());
while (calendar.getTime().before(contract.getEndDate()))
{
++numberOfDays;
calendar.add(Calendar.DAY_OF_YEAR, 1);
}
return numberOfDays;
}
}
FlatRatePricingStrategy.java
package rental;
/**
* A simple pricing strategy: every contract, every customer pays a flat rate
* Date: Jan 27, 2007
* Time: 7:51:22 PM
*/
public class FlatRatePricingStrategy extends AbstractPricingStrategy
{
protected double price;
public FlatRatePricingStrategy(double price)
{
if (price < 0.0)
throw new IllegalArgumentException("price cannot be negative");
this.price = price;
}
public double calculatePrice(Contract contract)
{
return price;
}
}
ConstantDailyRatePricingStrategy.java
package rental;
/**
* Constant daily rate treats the price as dollars per day
* Date: Jan 27, 2007
* Time: 8:19:03 PM
*/
public class ConstantDailyRatePricingStrategy extends FlatRatePricingStrategy
{
public ConstantDailyRatePricingStrategy(double price)
{
super(price);
}
public double calculatePrice(Contract contract)
{
return super.calculatePrice(contract)*getNumberOfDays(contract);
}
}
DiscountPricingStrategy.java
package rental;
import java.util.Arrays;
import java.util.Calendar;
import java.util.List;
/**
* Pricing strategy that gives a percentage discount on special days
* Date: Jan 27, 2007
* Time: 7:52:04 PM
*/
public class DiscountPricingStrategy extends FlatRatePricingStrategy
{
private static final List<Integer> DISCOUNT_DAYS = Arrays.asList( Calendar.MONDAY, Calendar.TUESDAY, Calendar.SATURDAY);
private double percentage;
public DiscountPricingStrategy(double price, double percentage)
{
super(price);
this.percentage = percentage;
}
public double calculatePrice(Contract contract)
{
double total = 0.0;
Calendar calendar = Calendar.getInstance();
calendar.setTime(contract.getBegDate());
while (calendar.getTime().before(contract.getEndDate()))
{
if (DISCOUNT_DAYS.contains(calendar.get(Calendar.DAY_OF_WEEK)))
{
total += price*(1.0-percentage);
}
else
{
total += price;
}
calendar.add(Calendar.DAY_OF_YEAR, 1);
}
return total;
}
}
MinimumDaysPricingStrategy.java
package rental;
/**
* Pricing strategy that enforces a minimum number of days rule
* Date: Jan 27, 2007
* Time: 9:20:24 PM
*/
public class MinimumDaysPricingStrategy extends FlatRatePricingStrategy
{
private int minNumberOfDays;
public MinimumDaysPricingStrategy(double price, int minNumberOfDays)
{
super(price);
if (minNumberOfDays < 0)
throw new IllegalArgumentException("minimum number of days cannot be negative");
this.minNumberOfDays = minNumberOfDays;
}
public double calculatePrice(Contract contract)
{
return super.calculatePrice(contract)*Math.max(minNumberOfDays, getNumberOfDays(contract));
}
}
RentalAgency.java
package rental;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.text.ParseException;
import java.text.NumberFormat;
import java.util.Date;
/**
* Rental agency model
* Date: Jan 27, 2007
* Time: 8:02:08 PM
*/
public class RentalAgency
{
public static final String DEFAULT_MAKE = "Toyota";
public static final String DEFAULT_MODEL = "Camry";
public static final int DEFAULT_YEAR = 2007;
public static final DateFormat DEFAULT_DATE_FORMAT = new SimpleDateFormat("dd-MMM-yyyy");
public static final double DEFAULT_DAILY_RATE = 50.0; // dollars per day or flat rate in dollars
public static final double DEFAULT_PERCENT_DISCOUNT = 0.10; // ten percent discount on discount days
public static final int DEFAULT_MIN_DAYS = 7; // default minimum number of days; gotta take a vehicle for a week.
public static void main(String [] args)
{
try
{
if (args.length > 3)
{
String first = args[0];
String last = args[1];
Date begDate = DEFAULT_DATE_FORMAT.parse(args[2]);
Date endDate = DEFAULT_DATE_FORMAT.parse(args[3]);
Customer customer = new Customer(new Name(first, last), new Address());
Vehicle vehicle = new Vehicle(DEFAULT_MAKE, DEFAULT_MODEL, DEFAULT_YEAR);
Contract contract = new Contract(customer, vehicle, begDate, endDate);
//PricingStrategy pricingStrategy = new FlatRatePricingStrategy(DEFAULT_DAILY_RATE);
//PricingStrategy pricingStrategy = new ConstantDailyRatePricingStrategy(DEFAULT_DAILY_RATE);
//PricingStrategy pricingStrategy = new DiscountPricingStrategy(DEFAULT_DAILY_RATE, DEFAULT_PERCENT_DISCOUNT);
PricingStrategy pricingStrategy = new MinimumDaysPricingStrategy(DEFAULT_DAILY_RATE, DEFAULT_MIN_DAYS);
System.out.println(contract);
System.out.println("# days: " + pricingStrategy.getNumberOfDays(contract));
System.out.println("price: " + NumberFormat.getCurrencyInstance().format(contract.getPrice(pricingStrategy)));
}
else
{
System.out.println("Usage: rental.RentalAgency [first] [last] [start] [end]");
}
}
catch (ParseException e)
{
e.printStackTrace();
}
}
}
