#6_Methods for Classes_14.ppt

Method Templatepublic class CoffeeReceipt { private String kind; private double pricePerPound; private double weight; public CoffeeReceiptString kind, double pricePerPound, double weight

Methods for Classes

Week 5

HOW TO DESIGN CLASS

HIERARCHIES

Basic Java Programming

Course material developed by Mai Anh Tho (tho@hcmuaf.edu.vn)

• Designing a good data representation for

a problem is the first step toward the

design of a good program, but it isn't

enough We also need functions that

compute results from some given data In

an object-oriented language, functions are implemented as METHODS Designing

methods proceeds in the fashion as

designing functions, which we are familiar

with from How to Design Programs

At a Specialty Coffee Seller

Problem Statement

• Develop a program that computes the cost

of selling bulk coffee at a specialty coffee seller from a receipt that includes the kind

of coffee, the unit price , and the total

amount ( weight ) sold

Method Template

public class CoffeeReceipt {

private String kind;

private double pricePerPound;

private double weight;

public CoffeeReceipt(String kind, double pricePerPound, double weight) {

}

Add a contract,

a purpose statement

METHOD SIGNATURE

Method Implementation

public class CoffeeReceipt {

private String kind;

private double pricePerPound;

private double weight;

public CoffeeReceipt(String kind, double pricePerPound, double weight) {

this.kind = kind;

this.pricePerPound = pricePerPound;

this.weight = weight;

}

// to compute the total cost of this coffee purchase [ in cents]

public double sellingCost() {

return this.pricePerPound * this.weight;}

}

public class TestCoffeeReceipt extends TestCase {

public void testConstructor() {

new CoffeeReceipt("Hawaiian Kona", 15.95, 100);

new CoffeeReceipt("Ethiopian", 8.00, 1000);

new CoffeeReceipt("Colombian Supreme ", 9.50, 1700);

}

public void testSellingCost() {

CoffeeReceipt hk = new CoffeeReceipt("Hawaiian Kona", 15.95, 100);

New Requirement

• Requirement: The coffee shop owner

may wish to find out whether a coffee sale involved more than a certain number of

pounds.

• Q: Supplement the class diagram to

include this requirement to the current

design

Class Diagram

• Q: Develop some examples for weighsMore()

// should produce → true

Q: Write a template for weighsMore() and implement

it

weighsMore() Template

public class CoffeeReceipt {

private String kind;

private double pricePerPound;

private double weight;

weighsMore() Implementation

public class CoffeeReceipt {

private String kind;

private double pricePerPound;

private double weight;

…

public boolean weighsMore( double amount ) {

return this. weight > amount ;

}

}

• Q: Write a unit test for weighsMore()

Unit Test for weighsMore()

public class CoffeeReceiptTest extends TestCase {

…

public void testWeighsMore() {

Assert.assert False (new CoffeeReceipt("Hawaiian Kona“,

Another New Requirement

• Requirement: A coffee shop customers want to

determine whether one coffee is cheaper than some other coffee (by comparing the price per pound)

• Q: Supplement the class diagram to include this

requirement to the current design

Class Diagram

• Q: Develop some examples for isCheaperThan()

1 new CoffeeReceipt("Hawaiian Kona“, 15.95 , 100)

.isCheaperThan(new CoffeeReceipt("Ethiopian", 20.00 , 100))

// should produce → true

2 new CoffeeReceipt("Hawaiian Kona“, 15.95 , 200)

.isCheaperThan(new CoffeeReceipt("Ethiopian", 15.95 , 100))

// should produce → false

3 new CoffeeReceipt("Hawaiian Kona“, 15.95 , 300)

.isCheaperThan(new CoffeeReceipt("Ethiopian", 8.00 , 100))

// should produce → false

Q: Write a template for isCheaperThan() and implement it

public class CoffeeReceipt {

private String kind;

private double pricePerPound;

private double weight;

…

public boolean isCheaperThan( CoffeeReceipt that ) {

return this. pricePerPound < that.pricePerPound ;

}

}

• Q: Write a unit test for isCheaperThan()

Unit Test for IsCheaperThan()

public class CoffeeReceiptTest extends TestCase {

…

public void testIsCheaperThan() {

Assert.assertTrue(new CoffeeReceipt("Hawaiian Kona“, 15.95, 100)

}

Another New Requirement

• The coffee shop customers want to

determine whether one coffee receipt

costs less than some other coffee receipt

+ boolean weighsMore(double amount)

+ boolean isCheaperThan(CoffeeReceipt that)+ boolean costsLessThan(CoffeeReceipt that)

Class Diagram

1 new CoffeeReceipt("Hawaiian Kona", 15.95, 100)

.costsLessThan(new CoffeeReceipt("Ethiopian“, 8.00, 1000))// should produce

→ false

public class CoffeeReceipt {

private String kind;

private double pricePerPound;

private double weight;

…

public boolean costsLessThan( CoffeeReceipt that ) {

return this sellingCost() < that sellingCost() ;

}

}

Unit Test for costsLessThan()

public class CoffeeReceiptTest extends TestCase {

…

public void testCostsLessThan() {

CoffeeReceipt hk = new CoffeeReceipt("Hawaiian Kona", 15.95, 100);

CoffeeReceipt e = new CoffeeReceipt("Ethiopian", 8.00, 1000);

CoffeeReceipt cs = new CoffeeReceipt("Colombian Supreme ", 9.50, 1700);

Exercise 3.1.2

• Study this class definition:

public class Image {

private int height; // pixels

private int width; // pixels

private String fileName;

private String quality; // low, medium, or high

public Image(int height, int width, String fileName, String quality) {

• And here are some examples

new Image(5, 10, "small.gif", "low");

new Image(120, 200, "med.gif", "low");

new Image(1200, 1000, "large.gif", "high");

Exercise 3.1.2 (cont.)

Develop the following methods for this class:

1 isPortrait, which determines whether the

image is taller than wider;

2 size, which computes how many pixels

the image contains;

3 isLarger, which determines whether one

image contains more pixels than some

other image.

Solutions

Exercise 3.1.3

Develop a Java class called House for this problem:

Develop a "real estate assistant'' program The "assistant'' helps the real estate agent locate houses of interest for clients The information about a house includes its kind, the number of rooms, its address, and the asking price An address consists of a house number, a street name, and a city Represent the following examples using your classes:

1 Ranch, 7 rooms, $375,000, 23 Maple Street, Brookline

2 Colonial, 9 rooms, $450,000, 5 Joye Road, Newton

3 Cape, 6 rooms, $235,000, 83 Winslow Road, Waltham

Develop the following methods for the class House:

• hasMoreRooms, which determines whether one house has more rooms

than some other house;

• inThisCity, which checks whether the advertised house is in some given

city (assume we give the method a city name);

• sameCity, which determines whether one house is in the same city as

some other house

Don't forget to test these methods. Solutions

day's run .For each entry, the program should compute

how fast the runner ran in minutes per mile .Develop a

method that computes the pace for a daily entry.

Solutions

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

Solutions

Extended Exercises

(Lab hours)

Exercise 3.1.6

• Modify the CoffeeReceipt class so that

sellingCost() takes into account bulk discounts: Develop a program that computes the cost of

selling bulk coffee at a specialty coffee seller

from a receipt that includes the kind of coffee,

the unit price, and the total amount (weight) sold

If the sale is for less than 5,000 pounds, there is

no discount For sales of 5,000 pounds to

20,000 pounds, the seller grants a discount of

10% For sales of 20,000 pounds or more, the

discount is 25% .

Don't forget to adapt the examples, too.

Exercise 3.1.7

• Design the method sizeString() for the Image

class It produces one of three strings,

depending on the number of pixels in the image:

• “small” for images with 10,000 pixels or fewer;

• “medium” for images with between 10,001 and 1,000,000 pixels;

• “large” for images that are even larger than that.

Relax &

GOOD JOB !

Solution 3.1.2

Solution 3.1.2: isPortrait()

• Method implementation

public boolean isPortrait() {

return this.width < this.height;

}

• Unit testing

public void testIsPortrait() {

Assert.assertFalse(new Image(5, 10, "small.gif", "low“).isPortrait());

Assert.assertFalse(new Image(120, 200, "med.gif", "low").isPortrait()); Assert.assertTrue(new Image(1200, 1000, "large.gif", "high").isPortrait());

}

Solution 3.1.2: size()

• Method implementation

public int size() {

return this.height * this.width;

}

• Unit testing

public void testSize() {

Assert.assertEquals(new Image(5, 10, "small.gif", "low").size(), 50); Assert.assertEquals(new Image(120, 200, "med.gif", "low").size(),

24000);

Assert.assertEquals(new Image(1200, 1000, "large.gif", "high").size(),

1200000);

}

Solution 3.1.2: isLarger()

• Method implementation

public boolean isLarger(Image that) {

return this.size() > that.size();

}

• Unit testing

public void testIsLarger() {

Image img1 = new Image(5, 10, "small.gif", "low");

Image img2 = new Image(120, 200, "med.gif", "low");

Image img3 = new Image(1200, 1000, "large.gif", "high");

Assert.assertFalse(img1.isLarger(img2));

Assert.assertTrue(img3.isLarger(img2));

}

Back

Solution 3.1.3

Solution 3.1.3: House

public class House {

private String kind;

private int nRooms;

private Address address;

private int price;

public House(String kind, int nRooms, Address address, int price) {

Solution 3.1.3: Address

public class Address {

private String houseNumber;

private String street;

private String city;

public Address(String houseNumber, String street, String city) {

Solution 3.1.3: hasMoreRooms()

• Method implementation

public boolean hasMoreRooms(House that) {

return this.nRooms > that.nRooms;

}

• Unit testing

public void testHasMoreRooms() {

House house1 = new House("Ranch", 7,

new Address("23", "Mapple Street", "Brooklyn"), 375000);

House house2 = new House("Colonial", 9,

new Address("5", "Jove Road", "Newton"), 450000);

House house3 = new House("Cape", 6,

new Address("83", "Winslow Road", "Waltham"), 235000);

Assert.assertFalse(house1.hasMoreRooms(house2));

Assert.assertTrue(house2.hasMoreRooms(house3));

}

public void testThisCity() {

House house1 = new House("Ranch", 7,

new Address("23", "Mapple Street", "Brooklyn"), 375000);

House house2 = new House("Colonial", 9,

new Address("5", "Jove Road", "Newton"), 450000);

House house3 = new House("Cape", 6,

new Address("83", "Winslow Road", "Waltham"), 235000);

Assert.assertTrue(house1.thisCity("Brooklyn"));

Assert.assertFalse(house1.thisCity("Newton"));

}

public void testSameCity() {

House house1 = new House("Ranch", 7,

new Address("23", "Mapple Street", "Brooklyn"), 375000);

House house2 = new House("Colonial", 9,

new Address("5", "Jove Road", "Newton"), 450000);

House house3 = new House("Cape", 6,

new Address("83", "Winslow Road", "Waltham"), 235000);

Assert.assertTrue(house1.sameCity(house1));

Assert.assertFalse(house1.sameCity(house2));

}

Back

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");

Solution 3.1.5

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);

• A ranch is a large farm used for raising

animals, especially cattle, horses or

sheep.

Back

• A colonial building or piece of furniture was built or made in a style that was popular in American in the 17th and 18th

centuries.

• A cape is a large piece of land that sticks out into the sea from the coast.