SSD3-U1S2

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Object-Oriented Programme Object-Oriented Programme 11

SSD3: Object-Oriented Programming and SSD3: Object-Oriented Programming and Design Design

1.1 Java Application 1.2 Designing Classes

Unit 1. Class DesignUnit 1. Class Design

1.2 Designing Classes1.2 Designing Classes

Contents 1.2.1 UML Class Diagrams 1.2.2 Relationships Between Classes 1.2.3 Common Class Structures 1.2.4 UML with Eclipse 1.2.5 Modeling Classes 1.2.6 Modeling the Library System

Assessments Practical Quiz 3 Practical Quiz 4 Multiple-Choice Quiz 2 Exercise 2

1.21.2.1 UML Class Diagrams .1 UML Class Diagrams

Introduction Class Notation

IntroductionIntroduction

The Unified Modeling Language (UML) is a graphical language for modeling the static and dynamical aspects of a system. unifies the best engineering practices for modeling

systems defines different graphical diagrams that provide multiple

perspectives of a system under development UML is a unification of the methodologies developed by

Grady Booch, James Rumbaugh, and Ivar Jacobsen. The Object Management Group (OMG), a not-for-profit

organization that promotes the use of object-oriented technology, has responsibility for the further development of the UML standard.

UML DiagramsUML Diagrams

Use case diagram ( 用例图 ) Class diagram ( 类图 ) Object diagrams ( 对象图 ) Behavior diagrams:

Statechart diagram ( 状态图 ) Activity diagram ( 活动图 ) Interaction diagrams:

Sequence diagram ( 顺序图 ) Collaboration diagram ( 协作图 )

Implementation diagrams: Component diagram ( 组件图 ) Deployment diagram ( 部署图 )

Class Notation Class Notation 类的表示符号类的表示符号 A class

represented by a rectangle with three compartments.

The first compartment contains the name of the class; the second compartment describes the attributes of the

class; third compartment describes the methods of the class.

Sample Sample

From left to right

Representation of class Employee Abbreviated representation of class Employee Shortest form of class Employee Essential representation of class Employee

1.21.2.2 Relationships Between Classes .2 Relationships Between Classes

Associations One-way and Two-way Associations Multiplicity Aggregation Specialization/Generalization

Associations Associations 关联关联 An association represents the relationship between

two or more classes. A binary association is a relationship between two

classes. An object of a class requires an object of another

class to do its work. In UML, a binary association is represented by a

solid line that connects the two classes. E.g., In a classroom, a professor instructs students.

In a bank system, clients hold bank accounts.

One-Way and Two-Way Associations One-Way and Two-Way Associations

An association can be a one-way or two-way relationship. A one-way association indicates

the direction in which one can navigate from an object of one class to an object of another class.

A two-way association indicates bi-directional navigation between objects of two classes.

difference one-way association : the first class has a reference to an

object of the second class, but the second class does not have a reference to an object of the first class.

two-way association : each class contains a reference to an object of the other class.

UML samplesUML samples

UML indicates a one-way association with an arrow at the end of the association line.

The attribute in the first class that contains a reference to an object of the second class is also written at the end of the line.

One-way association between classes Car and Engine indicates that an engine is part of a car

samplessamples

the relationship between the classes Country, Government, and Capital the class Country has a reference to an object of

class Governmentthe class Country a reference to an object of

class Capital

A class can contain A class can contain more than one associationmore than one association with another class with another class

Two associations between classes Flight and Pilot, one association with the attribute pilot and another with the attribute coPilot.

Multiplicity Multiplicity 多重性多重性 Multiplicity

indicates the number of instances of a class that may be associated with a single instance of another class. E.g.,

one car has four tires and one engine one client holds one or more bank accounts.

The multiplicity can be specified with a single integer a range n..m, where n is the lower limit and m is the upper limit. “ * “ used to denote no upper limit.

The following are the most common multiplicities: 0..1 Zero or one instance 0..* or * Zero or more instances 1 Exactly one instance 1..* One or more instances

One-to-one Association One-to-one Association

In a one-to-one association, exactly one instance of each class is related with exactly one instance of the other class.

One-to-many Association One-to-many Association

In a one-to-many association between classes A and B, one instance of class A may be related with many instances of class B, but one instance of class B is related with exactly one instance of class A.

Many-to-many Association Many-to-many Association

In a many-to-many association between classes A and B, one instance of class A may be related with

many instances of class Bone instance of class B may be related with

many instances of class A.

Aggregation Aggregation 聚集聚集 Each instance of class A is composed by instances

of class B. An instance of class B is part of an instance of

class A. The instance of class A is called the aggregate( 聚

合体 ) The instance of class B is called the component( 部

件 ).

Aggregation in UMLAggregation in UML

Specialization/Generalization Specialization/Generalization 具象具象 // 抽象抽象 (( 继承继承 //泛化泛化 ))

Specialization/Generalization represents the is-a relationship. E.g., a whale is-a mammala client is-a person.

Specialization/generalization allows class A to be defined as specialization of another class B.

Class A is called the specialization class 特殊化类Whale, client

class B the generalization class. 一般化类Mammal, person

Specialization/Generalization Specialization/Generalization

Specialization/generalization represented in UML by adding a triangle next to

the generalization class:

specialization/generalization relationshipspecialization/generalization relationship

If there is a specialization/generalization relationship between classes A and B ,so if A is-a B, then all instances of class A are also

instances of class B. 教材书， java 程序设计 / 英语 / 大学物理书

An important consequence of this relationship is class A inherits all the features of class B. All the attributes and methods of class B are also

attributes and methods of class A.

specialization/generalization relationshipspecialization/generalization relationship

The following class diagram represents the relationships Client is-a Person and Employee is-a Person:

Sample noteSample note

They are specialization/generalization relationshipsthe attributes of class Person are also attributes

of classes Client and Employee. Each instance of class Client contains the attributes

name, age, address, and accounts; Each instance of class Employee contains the

attributes name, age, address, salary, and departments.

Example of a system of multimedia files Example of a system of multimedia files

includes images, audio, and text files. The classes are defined as follows:

1.21.2.3 Common Class Structures.3 Common Class Structures

Introduction Collections Self-Containing Classes Relationship Loops

IntroductionIntroduction

Although the definition of classes and their relationships depends on the particular application, some class structures are common to many designs.

These class structures, which can be thought of as basic building blocks, can be composed to design complex systems. Like the the building a skyscraper

CollectionsCollections

A collection models a one-to-many relationship.

Collections store many instances of one class.

samplesample

The diagram uses a collection to represent the relationship

"one client holds one or more bank accounts"defines methods to handle the collection of

BankAccount instances. Each BankAccount instance in the collection has an

index indicating its location in the collection.

Self-Containing Classes Self-Containing Classes 自包含自包含 A class can have an association with itself.

the class contains attributes with references to objects of the same class.

samplesample

Class Person in a genealogical tree ( 家族系谱树 )system.

The relationships "each person has one mother" and "each person has one father" are indicated with the attributes mother and father.

The attributes mother and father are references to objects of class Person.

Another example,Another example,

The relationship "each employee has one boss." The diagram indicates that the boss of an

employee is another employee.

Relationship Loops Relationship Loops 关系循环关系循环 Self-containment can be found in relationships that

include two or more classes.

exampleexample

A file system. A file system has folders, and folders contain

files or more folders, or both. We can define a class Folder, which contains a

collection of FolderItem objects:

1.21.2.4 UML with Eclipse .4 UML with Eclipse Introduction Create Project Create Folder Create New Class Diagram Create Class BankAccount Create Class Person Create Class Client Create Specialization/Generalization Relationship Create Association Relationship Export Image

1.21.2.5 Modeling Classes.5 Modeling Classes

Process of Modeling Classes Identifying Classes Identifying Relationships Identifying Attributes Identifying Methods Modeling Using UML

Process of Modeling ClassesProcess of Modeling Classes

Object-oriented design is the process of building an object model for a

system to be developed. An object model specifies

the classes attributesMethodsrelationships with other classes.

How to building an object model from a system specification?

The steps to create an object modelThe steps to create an object model

Identify classes of objects from the system specification.

Identify relationships between classes. Identify attributes of each class. Identify methods of each class. Model system using UML.

Identifying ClassesIdentifying Classes

identify classes is to analyze the textual description in the system specification.

In textual analysis, the nouns and the noun phrases often indicate objects and their classes. Singular nouns ( “book,” “library catalog,” and

“client“ ) and plural nouns ( ”users,” “books,” and “accounts” ) indicate classes. 单数与复数

Proper nouns ( “the ACME Bank” ) and nouns of direct reference ( “the person that owned the account” ) indicate objects. 专有名词与指代

The steps for identifying the classes - 1The steps for identifying the classes - 1

List all the nouns in the specification. Prune the list: 对列表进行裁剪

Convert plural nouns to their singular form. In an object model, class names are singular.

Eliminate nouns that represent objects. Replace them with generic nouns.

use "client" instead of "John Smith." Eliminate nouns that are class attributes.

If cannot identify the attributes of the noun, it is possible a class attribute.

Group the synonyms and then choose the best name for the class from the group. "user" and "client" are synonyms. In a bank system, the

best name is "client" because the system may have two types of users: the clients and the bank's employees.

The steps for identifying the classes - 2The steps for identifying the classes - 2

Select the classes that are relevant to the system. Look for more relevant classes. Search the

application domain for: Physical things. "person," "book," and "computer." Roles played by persons or organizations."employer" and "supplier." Objects that represents an occurrence or event. "system crash,"

"flight," and "mouse click." Objects that represent a relationship between other objects in the

model. "purchase" (related to "buyer," "seller," and "merchandise") and "marriage" (related to "man" and "woman").

People who carry out some function. "student" and "clerk." Places. "library," "classroom," and "bank." Collections of objects, people, resources, or facilities. "catalog" and

"group." Concepts or ideas that are intangible. 抽象名词 For example,

“money” and “bank account.”

The steps for Identifying Relationships - 1The steps for Identifying Relationships - 1

Create an n x n table where n is the number of classes. Label the rows and columns with the class

names.

identify the specialization/generalization relationships for each cell in the row A and column B, ask the following

questions: Is an instance of class A an instance of class B? Is an instance of class B an instance of class A?

Analyze the answerIf the answer to both questions is yes, then

the class names might be synonyms.If the answer to the first question is yes, then

class A is a specialization of class B. Mark the cell in the row A and column B with an S.

If the answer to the second question is yes, then class A is a generalization of class B. Mark the cell in the row A and column B with a G.

Identify the association relationships, evaluate each cell in the row A and column B: If there is no association between class A and class

B, mark the cell with an X. If there are one or more associations between class

A and class B, then insert the association attributes. “study," “buy," "ownedAccounts," and "clients."

The table told us …..The table told us …..

Shows the relationships "a client is a person that has one or more accounts."

Indicates that class Client is a specialization of class Person

Class Client has an association relationship with class Account.

Identifying Attributes Identifying Attributes

Look for adjectives and possessive phrases 所有格"the X of Y" and "Y's X" in the system

specification. "number of the account" and "client's name.“ Use knowledge of the application domain to define

the set of attributes needed for the system being developed. 问题领域的经验，可从专业人员那里获取

Identifying Methods Identifying Methods

To identify behaviors, look for verbs. "the client deposits money into the account“ indicates

that class Account should define a method deposit.

Use knowledge of the application domain to define the set of methods needed for the system being developed.

Identifying Methods Identifying Methods

除了以上的，还要利用开发者的经验一般的应用系统都有的方法 ( 或系统行为 )

Create and initialize new instances. Set and get values of attributes. Load to and save from persistent storage. Destroy instances. Perform calculations using an object's values. Output or display a result.

If there are any collections held by the object, include the methods needed to add, remove, and

access elements of these collections.

Modeling Using UML Modeling Using UML

Use class notation to represent classes Include attributes and methods.

Use link notation to describe association and specialization/generalization relationships between classes.

For associations, specify the multiplicity and the name of the attribute associated with the relationship.

1.21.2.6 Modeling the Library System .6 Modeling the Library System

Specification of the Library System Identifying Classes Identifying Relationships Identifying Attributes Identifying Methods Modeling Using UML

Specification of the Library System Specification of the Library System 规格说明规格说明 The library system tracks the items checked out by

borrowers. The system contains a catalog of the items owned

by the library. There are two kinds of catalog items: books and recordings. All catalog items are identified by a unique code. (If the library owns several copies of the same book or recording, each copy has a unique code.) The information for each item includes title, year, and availability. An item is available if it is not checked out.

Specification of the Library SystemSpecification of the Library System

In addition: The information for a book includes the author and

number of pages. The information for a recording includes the

performer and format (CD or tape). The system contains a database of the borrowers.

Each borrower has a unique identification code in addition to a name. The system maintains a list, for each borrower, of the catalog items checked out.

Specification of the Library SystemSpecification of the Library System In the library system, the user should be able to:

Display the catalog by listing the code, title, and availability of each item.

Display a catalog item. Display the borrowers by listing the identification

code and name of each borrower. Display the catalog items checked out by a

borrower. Check out a catalog item by adding the item to

borrower's list of borrowed items. Check in a catalog item by removing the item

from borrower's list of borrowed items.

Identifying ClassesIdentifying Classes

First, we list the nouns in the system specification:

library system book CD

items recording tape

borrowers copy database

system information borrower

catalog item identification code

library title name

kinds year list

catalog items availability user

books author (borrower) code

audio items number of pages list of borrowed items

(item) code performer

copies format

Identifying ClassesIdentifying Classes Then, we prune the list by eliminating the following nouns:

(item) code, title, year, availability These nouns are attributes of a catalog item.

author, number of pages These nouns are attributes of a book.

performer, format These nouns are attributes of an audio item.

CD, tape These nouns are values for the attribute format.

name, identification code, (borrower) code

These nouns are attributes of a borrower.

userThis noun is an element outside the library

system.

information This noun is a generic term for the class attributes.

kinds This noun is not relevant to the system.

Identifying ClassesIdentifying Classes Next, we group the synonyms and then choose the best name

for the class from each group:

CatalogItem items, catalog items, copies, copy, item

LibrarySystem library system, system, library

Borrower borrowers, borrower

Book books, book

Recording recordings, recording

BorrowedItems list, list of borrowed items

Finally, we have ……Finally, we have ……

classes that are relevant to the systemLibrarySystem

Catalog CatalogItem Book RecordingBorrower BorrowedItems BorrowerDatabase

Identifying Relationships Identifying Relationships

table identifies the association and specialization/generalization relationships:

Identifying AttributesIdentifying Attributes

The following is the list of attributes for each class:

Class Attributes

LibrarySystem catalog, borrowerDB

Catalog items

CatalogItem code, title, year, available

Book author, numberOfPages

Recording performer, format

Borrower name, id, borrowedItems

BorrowedItems items

BorrowerDatabase borrowers

Identifying MethodsIdentifying Methods

The following is the list of methods for each class:

Class Methods

LibrarySystem

displayCatalog() ， displayCatalogItem(),displayBorrowerDatabase(),displayBorrower(),checkIn(),checkOut()

Catalog addItem(item:CatalogItem)getItem(index:int):CatalogItem getNumberOfItems():Int getItem(code:String):CatalogItem

CatalogItem getCode():StringgetTitle():StringgetYear():intisAvailable():booleansetAvailable(value:boolean)

Class Methods

Book getAuthor():StringgetNumberOfPages():int

Recording getPerformer():StringgetFormat():String

Borrower getId():StringgetName():StringgetBorrowedItems():BorrowedItems

Class Methods

BorrowedItems addItem(item:CatalogItem)removeItem(item:CatalogItem)getItem(index:int):CatalogItemgetItem(code:String):CatalogItemgetNumberOfItems():int

BorrowerDatabase

addBorrower(borrower:Borrower)getBorrower(index:int):BorrowergetNumberOfBorrowers():intgetBorrower(id:String):Borrower

Modeling Using UMLModeling Using UML

The following is a class diagram for the library system:

SSD3-U1S2

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