SYSTEM DESIGN

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SYSTEM DESIGN

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... the use of CRC cards for class discovery ... Use CRC cards to find classes, responsibilities, and ... CRC Cards for Printing Invoice. Printing an Invoice ... – PowerPoint PPT presentation

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Title: SYSTEM DESIGN

1
CHAPTER 16

SYSTEM DESIGN

2
CHAPTER GOALS

To learn about the software life cycle
To learn how to discover new classes and methods
To understand the use of CRC cards for class
discovery
To be able to identify inheritance, aggregation,
and dependence relationships between classes
To master the use of UML class diagrams to
describe class relationships
To learn how to use object-oriented design to
build complex programs

3
Software Life Cycle

Encompasses all activities from initial analysis
until obsolescence

4
Development Process

Analysis
Design
Implementation
Testing
Deployment

5
Analysis

Decide what the project is suppose to do
Output requirements document

6
Design

Plan how to implement the system
Output
description of classes and methods
diagrams showing the relationships among the
classes

7
Implementation

Write and compile the code
Output completed code

8
Testing

Run tests to verify the program works correctly
Output a report of the tests and their results

9
Deployment

Install the program and begin using it

10
The Waterfall Model
11
The Spiral Model

Describes an iterative process in which design
and implementation are repeated

12
The Spiral Model
13
Extreme Programming

Development methodology that strives for
simplicity by removing formal structure and
focusing on best practices

14
Extreme Programming

Realistic planning
Customers make business decisions
Programmers make technical decisions

15
Extreme Programming

Small releases
Release a useful system quickly
Release updates on a short cycle

16
Extreme Programming

Metaphor
A shared story to explain the system

17
Extreme Programming

Simplicity
Design as simply as possible instead of preparing
for future complexities

18
Extreme Programming

Testing
Programmers and customers write test cases
Test continuously

19
Extreme Programming

Refactoring
Restructure the system continuously to improve
code and eliminate duplication

20
Extreme Programming

Pair programming
Two programmers write code on the same computer

21
Extreme Programming

Collective ownership
All programmers change all code as needed

22
Extreme Programming

Continuous integration
Build the entire system and test it whenever a
task is complete

23
Extreme Programming

40-hour week
Don't cover up unrealistic schedules with heroic
effort

24
Extreme Programming

On-site customer
A customer is accessible to the programming team
at all times

25
Extreme Programming

Coding standards
Follow standards that emphasize self-documenting
code

26
Object-Oriented Design

Discover classes
Determine responsibilities of each class
Describe the relationships among the classes

27
Discovering Classes

A class represents some useful concept
Find classes by looking for nouns in the task
description
Define the behavior for each class
Find methods by looking for verbs in the task
description

28
CRC Card

Stands for classes, responsibilities,
collaborators
Use an index card for each class
Pick the class that should be responsible for
each method (verb)
Write the responsibility onto the class card
Indicate what other classes are needed to fulfill
the responsibility - the collaborators

29
A CRC Card
30
Relationships Between Classes

Inheritance
Association
Dependency

31
"Is-a" Relationship

The "is-a" relationship is inheritance use
extends
a circle is an ellipse
a car is a vehicle

32
"Has-a" Relationship

The "has-a" relationship is association use an
instance variable
a tire has a circle as its boundary
a car has a set of tire

33
Uses Relationship

The "uses" relationship is dependency
an Applet uses a Graphics object

34
"is-a" and "has-a"Example

class Car extends Vehicle //inheritance "is-a"
...
private Tire tires //association "has-a"

35
Association and Dependency

One class is associated with another if you can
navigate from its objects to objects of the
other class
One class depends on another if it comes into
contact with the other class in some way.
Association is a stronger form of dependency

36
UML Notation for Inheritance and Association
37
UML Relationship Symbols
38
Five-Part Development Process

Gather requirements
Use CRC cards to find classes, responsibilities,
and collaborators
Use UML diagrams to record class relationships
Use javadoc to document method behavior
Implement your program

39
Printing an Invoice - Requirements

Print billing address, all line items, amount due
Line item contains description, unit price,
quantity ordered, total price

40
Sample Invoice

INVOICE
Sam's Small
Appliances
100 Main Street
Anytown, CA
98765
Description Price Qty Total
Toaster 29.95 3 89.85
Hair dryer 24.95 1 24.95
Car vacuum 19.99 2 39.98
Amount Due
154.78

41
Printing an Invoice - CRC Cards

Discover classes
Nouns are possible classes
Invoice Price
Address Quantity
Item Total
Product AmountDue
Description

42
Printing an Invoice - CRC Cards

Classes after a process of elimination
Invoice
Address
Item
Product

43
CRC Cards for Printing Invoice
44
CRC Cards for Printing Invoice
45
CRC Cards for Printing Invoice
46
CRC Cards for Printing Invoice
47
Printing an Invoice - UML Diagrams

The relationship between Invoice classes

48
Printing an Invoice - Method Documentation

Use javadoc documentation comments to record the
behavior of the classes
Leave the body of the methods blank
Run the javadoc utility to obtain a formatted
version of the documentation in HTML format

49
Method Documentation Invoice class

/
Describes an invoice for a set of purchased
products.
/
class Invoice
/
Adds a charge for a product to this
invoice.
_at_param aProduct the product that the
customer ordered
_at_param quantity the quantity of the product
/
public void add(Product aProduct, int
quantity)
/
Formats the invoice.
_at_return the formatted invoice

/
public String format()
/
Computes the total amount due.
_at_Return the amount due
/
public double getAmountDue()

51
Method Documentation - Item class

/
Describes a quantity an article to purchase
and its price.
/
Class Item
/
Computes the total cost of this item.
_at_Return the total price
/
public double getTotalPrice()
/
Formats this item.
_at_Return a formatted string of this item
/

public String format()

53
Method Documentation - Product class

/
Describes a product with a description and a
price
/
class Product
/
Gets the product description.
_at_Return the description
/
public String getDescription()
/
Gets the product price.
_at_Return the unit price
/
public double getPrice()

54
Method Documentation - Address class

/
Describes a mailing address.
/
Class Address
/
Formats the address.
_at_Return the address as a string with 3
lines
/
public String format()

55
The Class Documentation in the HTML Format
56
Printing an Invoice - Implementation

The UML diagram will give instance variables
Look for associated classes
They yield instance variables

57
Implementation

Invoice is associated with Address and Item
It will have Address and Item instance variables

58
Implementation

An Invoice has one Address.
Declare one Address instance variable.
private Address billingAddress

59
Implementation

An Invoice has multiple Items.
Use an ArrayList to hold Items.
private ArrayList items

60
File InvoiceTest.java

01 import java.util.Vector
02
03 /
04 This program tests the invoice classes by
printing
05 a sample invoice.
06 /
07 public class InvoiceTest
08
09 public static void main(String args)
10
11 Address samsAddress
12 new Address("Sam's Small
Appliances",
13 "100 Main Street", "Anytown",
"CA", "98765")
14
15 Invoice samsInvoice new
Invoice(samsAddress)
16 samsInvoice.add(new Product("Toaster",
29.95), 3)
17 samsInvoice.add(new Product("Hair
dryer", 24.95), 1)

18 samsInvoice.add(new Product("Car
vacuum", 19.99), 2)
19
20 System.out.println(samsInvoice.format())
21
22

62
File Invoice.java

01 import java.util.ArrayList
02
03 /
04 Describes an invoice for a set of
purchased products.
05 /
06 class Invoice
07
08 /
09 Constructs an invoice.
10 _at_param anAddress the billing address
11 /
12 public Invoice(Address anAddress)
13
14 items new ArrayList()
15 billingAddress anAddress
16
17

18 /
19 Adds a charge for a product to this
invoice.
20 _at_param aProduct the product that the
customer ordered
21 _at_param quantity the quantity of the
product
22 /
23 public void add(Product aProduct, int
quantity)
24
25 Item anItem new Item(aProduct,
quantity)
26 items.add(anItem)
27
28
29 /
30 Formats the invoice.
31 _at_return the formatted invoice
32 /
33 public String format()
34
35 String r " I N V
O I C E\n\n"
36 billingAddress.format()

38 for (int i 0 i lt items.size() i)
39
40 Item nextItem (Item)items.get(i)
41 r r nextItem.format() "\n"
42
43
44 r r "\nAMOUNT DUE "
getAmountDue()
45
46 return r
47
48
49 /
50 Computes the total amount due.
51 _at_return the amount due
52 /
53 public double getAmountDue()
54
55 double amountDue 0
56 for (int i 0 i lt items.size() i)

58 Item nextItem (Item)items.get(i)
59 amountDue amountDue
nextItem.getTotalPrice()
60
61 return amountDue
62
63
64 private Address billingAddress
65 private ArrayList items
66

66
File Item.java

01 /
02 Describes a quantity an article to
purchase and its price.
03 /
04 class Item
05
06 /
07 Constructs an item from the product and
quantity
08 _at_param aProduct the product
09 _at_param aQuantity the item quantity
10 /
11 public Item(Product aProduct, int
aQuantity)
12
13 theProduct aProduct
14 quantity aQuantity
15
16
17 /

18 Computes the total cost of this item.
19 _at_return the total price
20 /
21 public double getTotalPrice()
22
23 return theProduct.getPrice()
quantity
24
25
26 /
27 Formats this item.
28 _at_return a formatted string of this item
29 /
30 public String format()
31
32 final int COLUMN_WIDTH 30
33 String description theProduct.getDescr
iption()
34
35 String r description
36

38
39 int pad COLUMN_WIDTH -
description.length()
40 for (int i 1 i lt pad i)
41 r r " "
42
43 r r theProduct.getPrice()
44 " " quantity
45 " " getTotalPrice()
46
47 return r
48
49
50 private int quantity
51 private Product theProduct
52

69
File Product.java

01 /
02 Describes a product with a description and
a price
03 /
04 class Product
05
06 /
07 Constructs a product from a description
and a price.
08 _at_param aDescription the product
description
09 _at_param aPrice the product price
10 /
11 public Product(String aDescription, double
aPrice)
12
13 description aDescription
14 price aPrice
15
16
17 /

18 Gets the product description.
19 _at_return the description
20 /
21 public String getDescription()
22
23 return description
24
25
26 /
27 Gets the product price.
28 _at_return the unit price
29 /
30 public double getPrice()
31
32 return price
33
34
35 private String description
36 private double price

71
File Address.java

01 /
02 Describes a mailing address.
03 /
04 class Address
05
06 /
07 Constructs a mailing address.
08 _at_param aName the recipient name
09 _at_param aStreet the street
10 _at_param aCity the city
11 _at_param aState the 2-letter state code
12 _at_param aZip the ZIP postal code
13 /
14 public Address(String aName, String
aStreet,
15 String aCity, String aState, String
aZip)
16
17 name aName
18 street aStreet

19 city aCity
20 state aState
21 zip aZip
22
23
24 /
25 Formats the address.
26 _at_return the address as a string with 3
lines
27 /
28 public String format()
29
30 return name "\n" street "\n"
31 city ", " state " " zip
32
33
34 private String name
35 private String street
36 private String city
37 private String state

73
An Automatic Teller Machine - Requirements

ATM has
Keypad
Display
Buttons A,B,C
The button function depends on the state of the
machine.

74
Requirements

ATM is used by bank customers. A customer has a
Checking account
Savings account
Customer number
Pin

75
Requirements

At start up the customer is expected to
Enter customer number
Press the A button.
The display showsEnter Customer Number A OK

76
Requirements

The customer is expected to
Enter a PIN
Press A button.
The display showsEnter PINA OK

77
Requirements

Search for the customer number and PIN
If it matches a bank customer, proceed
Else return to start up screen

78
Requirements

If the customer is authorized
The display shows Select AccountA Checking
B SavingsC Exit

79
Requirements

If the user presses C
The Atm returns to the start up screen
If the user presses A or B
The ATM remembers which
The display shows Balance balance in selected
accountEnter amount and select transactionA
WithdrawB DepositC Cancel

80
Requirements

If the user presses A or B
The value entered is withdrawn or deposited.
The ATM reverts to previous state.
If the user presses C
The ATM reverts to previous state.

81
User Interface of the Automatic Teller Machine
82
An Automatic Teller Machine - CRC

Nouns are possible classes
ATM Bank account
User - same as Customer Checking account
Keypad Savings account
Display - use JTextArea Customer
Display message - use Strings Customer number
Button - use JButton PIN
State Bank

83
CRC Cards for Automatic Teller Machine
84
CRC Cards for Automatic Teller Machine
85
CRC Cards for Automatic Teller Machine
86
CRC Cards for Automatic Teller Machine
87
ATM States

START Enter customer ID
PIN Enter PIN
ACCOUNT Select account
TRANSACT Select transaction

88
State Diagram for ATM Class
89
The Relationships Between the ATM Classes
90
An Automatic Teller Machine - Method
Documentation

Use javadoc documentation comments to record the
behavior of the classes
Leave the body of the methods blank
Run the javadoc utility to obtain a formatted
version of the documentation in HTML format

91
Method Documentation ATM Class