Methods and containment arrows (lập TRÌNH cơ bản SLIDE)

Define Class, Constructor and test Constructorpublic class GPSLocation { private double latitude /* degrees */; private double longitude /* degrees */; public GPSLocationdouble latitude

Methods and Containment

Arrows

Week 4,5,6

Basic Programming Course

Date example

• Develop a program that helps you keep track

of daily One date is described with three

pieces of information: a day , a month , and a

Class

Define Class, Constructor and test Constructor

public class Date {

private int day;

private int month;

private int year;

public Date(int day, int month, int year) {

public class TestDate extends TestCase {

public void testConstrutor(){

new Date(5, 6, 2003); // denotes June 5, 2003

new Date(6, 6, 2003); // denotes June 6, 2003

new Date(23, 6, 2000); // denotes June 23, 2000

}

GPS Location example

• Develop a GPS navigation program for cars

The physical GPS unit feeds the program with the current location Each such location

consists of two pieces of information: the

latitude and the longitude

GPSLocation

- double latitude

- double longitude Property or field

Method Data type

Class

Define Class, Constructor and test Constructor

public class GPSLocation {

private double latitude /* degrees */;

private double longitude /* degrees */;

public GPSLocation(double latitude, double longitude) {

public class TestGPSLocation extends TestCase {

public void testConstrutor(){

new GPSLocation (33.5, 86.8);

new GPSLocation (40.2, 72.4);

new GPSLocation (49.0, 110.3);

}

Class

A class is a generic description of a “thing” It has:

1 Attribute: describes the “thing”

Attributes = Properties = Information = Fields = Data =

Variables

2 Behavior: describes what the “thing” does

Behaviors = Methods = Functions = Operations

3 State: describes the state that “thing” belongs to

A “thing” in a computer system ‘come alive – they

have behavior

Car example

With a Car

• Attributes which we concern: manufacturer, color, speed,…

• Behaviors can happen with a car: how to start

up, how to speed up,

• States:

state,

Book example

A Book in library has:

• Attributes that we concern : name, author, publisher, price,…

• Behaviors can modeled with this book: borrow, payback,…

• States:

– If it is ready to be borrow, it in ready state

– if it is borrowed, it becomes busy state

– when it is old, damaged and taken stock of, it is in out of stock (thanh lý) state.

– …

Room example

A Room in hotel has:

• Attributes we concern: name, kind (may be: usual, deluxe, VIP,…), price per day,…

• Behavior can happen with a room: rent,…

– If it is ready to be rent, it is in ready state

– if it is rent, it becomes busy state

state

– …

Point example

A point in monitor has:

which tells us where the pixel is located in the

• Behaivors:

– Computes how far some pixel is from the origin

– Computes the distance between 2 pixels,…

• State: ?

So, some real-life objects do not have state.

– Compute his average score.

– Check whether the student is supervised by some teacher,

– Transfer this student for another head teacher.

• State: ?

Rectangle example

With a Rectangle:

• Attributes that we concern: height, width,

north west point,…

– The book Nhat ky Dang Thuy Tram, author is Dang Thuy Tram,

published by Tuoi Tre, price 3$ is an instance of Book class.

– The deluxe room- No 201, price 50 $ per day is an instance of Room

class.

– A red point (2,3) is an instance of Point class.

– The student Nguyen Van A, his head teacher is Miss Thuy, has 8 in

Math, 9 in Physic and 7 in Chemistry is is an instance of Student class – A rectangle has height 5 cm, width 3 cm, north west point (2,3) is an

• None modifier: Classes in the same package

can access this attribute / method.

• public : Classes in all packages can access this

attribute / method.

• private : Only the class itself can access this

attribute / method.

The public or private modifiers

for attribute and method

Encapsulation

Group discussion

•Find more class examples in real life?

•Find more class examples in real life which

do not have behavior, then add their

behavior?

•Distinguish class and instance of class

(object).

Relax &

… Do Exercises …

Entry example

• Sometimes information not only consist of several pieces of information, but one of its constituents consists of several

pieces, too Take a look at this problem:

• Develop a program that manages a runner's training log Every day the runner enters one entry concerning the day's run

Each entry includes the day's date, the distance of the day's run, the duration of the run, and a comment describing the runner's post-run feeling

Define class and constructor

(define-struct Date (day

private int month;

private int year;

public Date(int day, int month, int year) { this.day=day;

this.month=month;

this.year=year;

} } public class Entry { private Date date;

private double distance;

private int durationInMinutes;

private String postRunFeeling;

public Entry(Date date, double distance, int durationInMinutes,String postRunFeeling ) { this.date=date;

this.distance=distance;

this.durationInMinutes=durationInMinutes; this.postRunFeeling=postRunFeeling;

} }

Date date1 = new Date(6, 6, 2004);

Date date2 = new Date(23, 6, 2004);

} } package entry;

Date date1 = new Date(6, 6, 2004);

new Entry(date1, 2.8, 24, "tired");

ran in minutes per mile .Develop a method that computes the pace for a daily entry.

Solution 3.1.4: pace()

• Method implementation

public double pace() {

return this.durationInMinutes / this.distance;

}

• Unit testing

public void testPace() {

Entry entry = new Entry(new Date(5, 6, 2004), 5.3, 27, "good");

Exercise 3.1.5

• A runner's log refers to Dates (see the figure) and a natural

question concerning comparing dates is when one occurs earlier than another one Develop a method that determines whether one date occurs earlier than another date

• Hint: The first possibility is that the first date is in the year

preceding the other Next, if the years are the same, the month in the first date is before the month in the second date Finally, if both the year and the month values are the same, the date in the first date is before the day in the second date

Method Implementation

public class Date {

private int day;

private int month;

private int year;

public Date(int day, int month, int year) { … }

public boolean earlierThan(Date that) {

if (this.year < that.year) return true;

if (this.year > that.year) return false;

if (this.month < that.month) return true;

if (this.month > that.month) return false;

if (this.day < that.day) return true;

return false;

}

}

Unit Testing

public void testEarlierThan() {

Date date1 = new Date(30, 6, 2003);

Date date2 = new Date(1, 1, 2004);

Date date3 = new Date(1, 12, 2004);

Date date4 = new Date(15, 12, 2004);

Date date5 = new Date(31, 12, 2004);

Exercise 3.1.5

• Develop a method that determines whether one entry occurs earlier than another entry.

• Q: Which class (Entry or Date) should we put ealierThan()

method in ?

• A: : Put ealierThan() in both classes

The ealierThan() method deals with properties of the Date so that we delegate this computational task to the corresponding methods in Date class

public vois testEalierThan(){

Entry e1= new Entry(new Date(5, 6, 2004), 5.3, 27, "good");

Date date1 = new Date(6, 6, 2004);

Entry e2 = new Entry(date1, 2.8, 24, "tired");

Date date2 = new Date(23, 6, 2004);

Entry e3 = new Entry(date2, 26.2, 159, "exhausted");

assertTrue(e1.ealierThan(e2));

assertFalse( e1.ealierThan(e1));

assertFalse(e3.ealierThan(e2));

}

Restaurant example

• Develop a program that helps a visitor navigate Manhattan's restaurant scene The program must be able to provide four pieces of information for each restaurant: its name , the kind of food it serves, its price range, and the closest intersection (street and avenue)

Delegation

• Q: Which class (Entry or Date) should we put ealierThan()

method in ?

• A: The ealierThan() method deals with properties of the Date

so that we delegate this computational task to the

corresponding methods in Date class

??? ealierThan(???)

Problem Statement

• Develop a method to help visitors to find out whether two restaurants are close to each

other

• Two restaurants are "close'' to each other if

they are at most one avenue and at most one

street away from each other

• Notice: This is an interesting example!

• Q: Add this method to the class diagram

avenue

S tr

ee t

Q: Which class (Restaurant or Intersection) should we put closeTo()

method in ?

A: Put closeTo() in both classes.

The closeTo() method deals with properties of the Intersection so

that we delegate this computational task to the corresponding

methods in Intersection class

new Intersection(3, 3).closeTo(new Intersection(3, 2))

// should produce ? true

new Intersection(3, 3).closeTo(new Intersection(3, 5))

// should produce false

new Intersection(3,3).closeTo(new Intersection(5, 4))

// should produce false

• Q: Create a template and then implement the method

closeTo() in the Intersection class

Template

public class Intersection {

private int avenue;

private int street;

public Intersection(int avenue, int street) {

Method Implementation

public class Intersection {

private int avenue;

private int street;

public Intersection(int avenue, int street) {

this.avenue = avenue;

this.street = street;

}

public boolean closeTo(Intersection that ) {

return ((Math.abs(this.avenue - that avenue) <=1) &&

(Math.abs(this.street - that street) <= 1));

}

}

• Q: Create examples for the method closeTo()

in the Restaurant class

Template

public class Restaurant {

private String name;

private String food;

private String priceRange;

private Intersection intersection;

public Restaurant(String name, String food, String priceRange,

public class Restaurant {

private String name;

private String food;

private String priceRange;

private Intersection intersection;

public Restaurant(String name, String food, String priceRange,

Unit Testing

public void testCloseTo() {

Restaurant r1 = new Restaurant("La Crepe", "French", "moderate",

Part I: Exercise 3.1.1 to 3.1.3 (HTDCH)

• Develop a program that can assist Amtrak customers with the

arrangement of train trips The available information about a specific train includes its schedule, its route, and whether it is local.

• The route information consists of the origin and the destination station.

• A schedule specifies the departure and the arrival (clock) times when the train leaves and when it arrives

• ClockTime consists of the hour (of the day) and the minutes (of the hour)

• The customer want to know:

– Does his destination station match the destination of the train trip?

– What time does the train start ?

– How long does the train trip take?

Extended Exercises

(Lab hours)

Prepare for next week

How to design class hierarchy

• III Fun Methods       

 4 Methods and Containment Arrow   

Relax &

… Do Exercises …

The rectangles are located on the Cartesian plane

of a computer canvas, which has its origin in the northwest corner

determine the shortest distance of the

Rectangle to the origin.

• This, in turn, means computing the distance between its northwest corner and the origin

northwest corner

Problem Analysis

We need two methods:

1 Measuring the distance of a Rectangle to the

A: Put distanceTo0 () in both classes.

The distanceTo0 () method deals with properties of the CartesianPoint

so that we delegate this computational task to the corresponding

methods in CartesianPoint class

• Q: Create a template and then implement the method

distanceToO() in the CartesianPoint class

public double distanceToO() {

return Math.sqrt (this.x * this.x + this.y * this.y);

}

}

Tips: Math.sqrt is the name of the method that computes the square root of its argument as a double.

• Q: Create examples for the method

distanceToO() in the Rectangle class

Examples

CartesianPoint p = new CartesianPoint(3,4);

Rectangle r = new Rectangle(p, 5, 17);

• Q: Create a template and then implement the method

distanceToO() in the Rectangle class

public class Rectangle {

private CartesianPoint northWestCorner;

private int width;

private int height;

public Rectangle(CartesianPoint northWestCorner, int width, int height) {

this.northWestCorner = northWestCorner;

this.width = width;

this.height = height;

}

public double distanceToO () {

this.northWestCorner.distanceToO()

this.width

this.height

}

Method Implementation

public class Rectangle {

private CartesianPoint northWestCorner;

private int width;

private int height;

public Rectangle(CartesianPoint northWestCorner, int width, int height) {

this.northWestCorner = northWestCorner;

this.width = width;

this.height = height;

}

public double distanceToO() {

return this.northWestCorner.distanceToO();

}

}

Unit Testing

public void testDistanceToO() {

CartesianPoint p = new CartesianPoint(3,4);

Rectangle r = new Rectangle(p, 5, 17);

Problem Extension Statement

• Compute the distance between the rectangle’s center and the origin

Solution 1

public class Rectangle {

private CartesianPoint northWestCorner;

private int width;

private int height;

public Rectangle(CartesianPoint northWestCorner, int width, int height) {

this.northWestCorner = northWestCorner;

this.width = width;

this.height = height;

}

public double distanceToO() {

return this.northWestCorner.distanceToO();

}

public double distanceFromCenterToO() {

double a = this.northWestCorner.getX() + this.width/2;

double b = this.northWestCorner.getY() + this.height/2;

public class CartesianPoint {

public double distanceToO() {

return Math.sqrt(this.x * this.x + this.y * this.y);

Solution 2

public class Rectangle {

private CartesianPoint northWestCorner;

private int width;

private int height;

public Rectangle(CartesianPoint northWestCorner, int width, int height) {

this.northWestCorner = northWestCorner;

this.width = width;

this.height = height;

}

public double distanceToO() {

returnthis.northWestCorner.distanceToO();

}

public double distanceFromCenterToO() {

returnthis.center.distanceToO();

}

}

• Q: How to find the value of the center?

Solution 2 (cont)

public class Rectangle {

private CartesianPoint northWestCorner;

private int width;

private int height;

public Rectangle(CartesianPoint northWestCorner, int width, int height) {

this.northWestCorner = northWestCorner;

this.width = width;

this.height = height;

}

public double distanceToO() {

return this.northWestCorner.distanceToO();

}

public CartesianPoint calculateCenter() {

double a = this.northWestCorner.getX() + this.width/2;

double b = this.northWestCorner.getY() + this.height/2;

return new CartesianPoint( (int)(a),(int)(b));

}

public double distanceFromCenterToO() {

+ int getY()

1

Circle example

• The circle are located on the Cartesian plane of a computer canvas, which has its center and radius

• Compute the distance form circle to the origin

• Computing the perimeter of a circle

• Computing the area of a circle (disk)

• Computes the area of a ring, which is this disk with a hole