Methods with effects (lập TRÌNH cơ bản SLIDE)

A2 Programming Course

Methods with effects
Week 14,15


Cyclical Data


Bookstore Manager’s Problem


A Variation of the Bookstore Manager’s
Problem
• Develop a program that assists a bookstore
manager. The manager's program should keep a
record for each book
• The record must include information about the
author, the book's title, its price, and its
publication year
• The information about the author includes
author's name, year of birth, and a list of books
written by this author
• Note: Remember to implement toString()


Examples
• The bookstore has the following books written by Jack
London, born 1876:
–
–

–
–

Call of the Wild (1903), published in 1995, $10
The Sea-Wolf (1904), published in 1999, $12
Martin Eden (1913), published in 1998, $12
White Fang (1906), published in 2001, $10

• The bookstore has the following books written by
Danielle Steel, born in 1955, all in their original edition:
–
–
–
–
–

Daddy (1989), $20
Heartbeat (1992), $15
Jewels (1993), $22
Wings (1995), $25
The Ghost (1995) $28


Class Diagram
Author
- String name
- int birthYear
- ALoBooks books
author

books
1..*

<<abstract>>
ALoBook s

rest
1

1

Empty

Cons
- Book first
- ALoBooks rest

first

1

Book
- Author author
- String title
- double price
- int publicationYear


Problem in Designing Constructors
• To create a new object in the class Book we need

to refer to the Author. But each Author refers to a
list of books
• Q: The egg comes first or the hen comes first?
• Solution: A reasonable solution is to define an
Author object with an empty list of books. Then,
as the author writes a new book, we create a Book
object, add it to the bookstore list of books, and
add this book to the author's list of books


public class AuthorTest extends TestCase {
public void test() {
Author jackLondon = new Author("Jack London", 1876);
Book cotw = new Book(jackLondon, "Call of the Wild", 1995, 10);
Book tsw = new Book(jackLondon, "The Sea-Wolf", 1999, 12);
Book me = new Book(jackLondon, "Martin Eden", 1998, 12);
Book wf = new Book(jackLondon, "White Fang", 2001, 10);
System.out.println(jackLondon);

}

}

Author danielleSteel = new Author("Danielle Steel", 1955);
Book d = new Book(danielleSteel, "Daddy", 1989, 20);
Book h = new Book(danielleSteel, "Heartbeat", 1992, 15);
Book j = new Book(danielleSteel, "Jewels", 1993, 22);
Book w = new Book(danielleSteel, "Wings", 1995, 25);
Book tg = new Book(danielleSteel, "The Ghost", 1995, 28);
System.out.println(danielleSteel);

public class Author {
private String name;
private int birthYear;
private ALoBooks books;
public Author(String name, int birthYear) {
this.name = name;
this.birthYear = birthYear;
this.books = new Empty();
}
String getName() {
return this.name;
}
public String toString() {
return this.name + ", " + this.birthYear + "\n" + this.books;
}
}


public class Book {
private Author author;
private String title;
private double cost;
private int publishYear;
public Book(Author author, String title, int publishYear, double cost) {
this.author = author;
this.title = title;
this.cost = cost;
this.publishYear = publishYear;

this.author.addBook(this);
}

}

public String toString() {
return this.author.getName() + ", " + this.title + ", " +
this.cost + ", " + this.publishYear + "\n";
}


addBook() in Author
// class Author
void addBook(Book book) {
this.books = this.books.add(book);
}


class ALoBooks
public abstract class ALoBooks {
public abstract ALoBooks add(Book book);
}


class Empty
public class Empty extends ALoBooks {
public ALoBooks add(Book book) {
return new Cons (book, new Empty());
}
public String toString() {

return "\n";
}
}


Class Cons
public class Cons extends ALoBooks {
private Book first;
private ALoBooks rest;
public Cons(Book first, ALoBooks rest) {
this.first = first;
this.rest = rest;
}
public ALoBooks add(Book book) {
return new Cons (book, this);
}

}

public String toString() {
return this.first + " " + this.rest;
}


New add(Book book) version
public abstract class ALoBooks {
public ALoBooks add(Book book){
return new Cons(book, this);
}
}

The Transportation Network
Problem


Problem Statement
• The Metropolitan Transit Agency has a web
site that allows the user to display information
about any of its stations and its train routes.
• The user may view the list of all stations along
a given route.
• The user may also find out what are all the
routes that serve a given station


Examples
• The list of stations is: Kenmore, Park, Center,
North, Science, Ashmont, Downtown, Charles,
State, Bowdoin, Maverick, Wonderland
• Green Line runs from Kenmore through Park,
Center, North to Science.
• Red Line runs from Ashmont through
Downtown and Park to Charles.
• Blue Line runs from Bowdoin through Center,
State, Maverick, to Wonderland


Ashmont

Downtown

State

Kenmore

Park

Center

Charles

Bowdoin

Maverick

Wonderland

North

Science


The Problem
• The class Station needs to have fields for its
name, and a list of Routes.
• The class Route needs to have a field for its
name, the origin, the destination, and for a
list of stations.
• Again, we cannot build a route without

knowing all the stations, but the station
should know what routes it serves.


Solution
• To create a representation of this data we first
build all station objects, omitting the route
information.
• Next, for each route, we first build a list of its
stations.
• Then, create the route object, and instruct the
constructor to notify every station that it now
serves this route, as well as the origin and
destination station.


Station
- String name
- ALoRoutes routes
first

1

routes
1

ALoRoutes

rest
1

2
origin, destination
EmptyLoRoutes

ConsLoRoutes
- Route first
- ALoRoutes rest

first

1

Route
- String name
- Station origin
- Station destination
- LoStations stations

stations

ALoStations

1

EmptyLoStations

rest
1

ConsLoStations
- Station first
- ALoStations rest


A Simpler Class Diagram

Station
- String name
- List routes

*

Route
- String name
- Station origin
* - Station destination
- List stations


public class RouteTest extends TestCase {
public void test() {
// create stations for green route
Station kentmore = new Station("Kentmore"); Station park = new Station("Park");
Station center = new Station("Center"); Station north = new Station("North");
Station science = new Station("Science");
// create green route
Route green = new Route("Green", kentmore, science);
green.addStation(park);
green.addStation(center);

green.addStation(north);
System.out.println(green);
// create stations for red route
Station ashmont = new Station("Ashmont");
Station charles = new Station("Charles");
Station downtown = new Station("Downtown");
// create red route
Route red = new Route("Red", ashmont, charles);
red.addStation(downtown);
red.addStation(park);
System.out.println(red);
// create stations for blue route
Station bowdoin = new Station("Bowdoin");
Station maverick = new Station("Maverick");

Station state = new Station("State");
Station wonderland = new Station("Wonderland");

// create blue route
Route blue = new Route("Blue", bowdoin, wonderland);
blue.addStation(center);
blue.addStation(state);
blue.addStation(maverick);
System.out.println(blue);

}

}

// print stations on green route

System.out.println(kentmore);
System.out.println(center);
System.out.println(science);

System.out.println(park);
System.out.println(north);

// print stations on red route
System.out.println(ashmont);
System.out.println(charles);

System.out.println(downtown);

// print stations on blue route
System.out.println(bowdoin);
System.out.println(maverick);

System.out.println(state);
System.out.println(wonderland);


public class Station {
private String name;
private ALoRoutes routes;
public Station(String name) {
this.name = name;
this.routes = new EmptyLoRoutes();
}
public String getName() {
return this.name;

}
public String toString() {
return "Station " + this.name + ": " + this.routes.getName();
}
}