Object-Oriented Programming (Java)
Topics Covered Today
• Unit 1.2 Designing Classes
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1.2.1 UML Class Diagrams
1.2.2 Relationships Between Classes
1.2.3 Common Class Structures
1.2.4 UML with Eclipse
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UML Introduction
• Programming is like building a house. An architect
creates a design, and a builder uses appropriate tools to
carry out the design. The builder does not proceed without
a blueprint from the architect.
• Software developers also need a blueprint to create
complex systems.
• The UML is a toolbox of graphical notations used to
produce the blueprint -- a graphical depiction of the
software design
• UML, Unified Modeling Language
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Unified Modelling Language (UML)
• A graphical language for
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Visualising
Specifying
Constructing
Documenting
• Object-oriented software systems
• OMG (Object Management Group国际对象管理
组织) is responsible for UML standard.
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UML
• UML is not a method. It does not outline a
procedure for designing software; it is a modeling
language that captures the design graphically.
• Whatever process you use, you can use UML to
record the results of your analysis and design
decisions.
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UML
• The main reason to use UML notation is
communication.
– To discuss design with someone, both need to
understand the modeling language, not the process
used to come up with the design.
– Human language is imprecise
– Code is too detailed
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UML Diagrams
• Use case diagram (用例图)
• Class diagram (类图)
• Behavior diagrams (行为图)
– Statechart diagram (状态图)
– Activity diagram (活动图)
– Interaction diagrams (交互图)
• Sequence diagram (顺序图)
• Collaboration diagram (协作图)
• Implementation diagrams (实现图)
– Component diagram (组件图)
– Deployment diagram (部署图)
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Class Notation
• A class is 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;
– and the third compartment describes the methods of the
class.
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UML Class Diagram
NameClass
-attribute1 : Type
-attribute2 : Type
name
attribute
method
+method1(param1 : Type, param2 : Type) : Type
+method2(param1 : Type, param2 : Type) : Type
• - private
• + public
• # protected
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Employee Class
• This class contains three private attributes:
– name
– hourlyWage
– hourWorked
• It also contains the following public methods:
– Methods to access the values of the attributes:
• getName, getHourlyWage, and getHoursWorked
– Methods to modify the values of the attributes:
• setName, setHourlyWage, and setHoursWorked
– A method to obtain the employee's earnings:
• getEarnings
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Representation of Employee
Employee
-name : String
-hourlyWage : Double
-hoursWorked : Double
+getName() : String
+getHourlyWage() : Double
+getHoursWorked() : Double
+setName(newName : String)
+setHourlyWage(newHourlyWage : Double)
+setHoursWorked(newHoursWorked : Double)
+getEarnings() : Double
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Abbreviated Representation (1)
Employee
-name : String
-hourlyWage : Double
-hoursWorked : Double
+getName()
+getHourlyWage()
+getHoursWorked()
+setName(newName : String)
+setHourlyWage(newHourlyWage : Double)
+setHoursWorked(newHoursWorked : Double)
+getEarnings()
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Abbreviated Representation (2)
Employee
Employee
-name : String
-hourlyWage : Double
-hoursWorked : Double
+getEarnings()
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Associations (关联)
• An association represents the relationship between two or more
classes.
– 关联就是类和类之间的关系。
• Association is represented by a solid line that connects the two
classes.
• For instance:
– a professor instructs students
Student
Professor
– clients hold bank accounts
Client
BankAccount
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One-way Associations (单向关联)
• In a 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.
– 单向关联中，第一个类中有一个第二个类的对象的
引用，但第二个类中没有第一个类的对象的引用
• UML indicates a one-way association with an
arrow at the end of the association line.
Car
Engine
-engine
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One-way Associations (单向关联)
• A class has associations with more than one class.
Country
-capital
-goverment
Goverment
capital
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One-way Associations (单向关联)
• A class can contain more than one association with
another class (一个类和另一个类可以有多个关
联)
Flight
-coPilot
-pilot
Pilot
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Two-way Associations(双向关联)
• A two-way association indicates bi-directional
navigation between objects of two classes.
– 双向关联中每个类都有另外一个类的对象的引用。
Course
-students
-courses
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Student
Multiplicity(多重性)
• Multiplicity indicates the number of instances of a class
that may be associated with a single instance of another
class.
– 多重性就是一个类有多少个实例与另外一个类的实例相关
联
– Car has four tires and one engine
– One client holds one or more bank accounts
– A professor can instruct more than one student
• The multiplicity can be specified with a single integer or
as a range
– n，n=1,2,3,…
– n…m，n代表最小值，m代表最大值
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Common multiplicities
0…1
Zero or one instance
0…* or *
Zero or more instances
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Exactly one instance
1…*
One or more instances
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Multiplicity
• States the number of objects that are connected
across the association.
– Unspecified
– Exactly one
– Zero or more (many, unlimited)
1
0..*
*
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1..*
One or more
Zero or one
Specified range
Multiple, disjoint ranges
0..1
2..4
2, 4..6
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One-to-one Association(一对一关联)
-engine
Car
1
1
-goverment
1
Engine
1
Country
1
1
Goverment
-capital
capital
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One-to-many Association(一对多关联)
-account
Client
Year
1…*
1
1
12
-months
1
Month
BankAccount
4…5
-weeks
Week
1
7
-days
Day
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Many-to-many Association(多对多关联)
• In a many-to-many association between classes A
and B, one instance of class A may be related with
many instances of class B, and one instance of
class B may be related with many instances of
class A.
Student
-student
0…*
-course
0…*
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Course
Many-to-many Association
• Find the association between Person and Company
Person
-employee
1…*
-employer
0…1
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Company
Many-to-many Association
Person
-employee
1
1…*
-employer
0…1
Company
“One person can work for
at most one employer.”
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Many-to-many Association
Person
-employee
1…*
-employer
1
0…1
Company
“One company has
at least one employee.”
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Many-to-many Association
• Find associations between Employee, Department
and Project.
1…*
Employee -employees
-participants
1…*
-projects
1…*
1…*
Department
-departments
Project
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Aggregation(聚集)
• Aggregation is a special form of association.
• Models a whole/part relationship.
• Represents a “has-a” relationship
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Aggregation Example
• A book is composed of one table of contents, zero
or one prefaces, one or more chapters, and one
index. In a book, each chapter is composed of one
or more sections, and each section is composed of
one or more paragraphs and zero or more figures.
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Aggregation hierarchy of a book
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Composition(合成)
• Models a whole/part relationship with a strong
ownership; when the whole dies, the part does so
as well.
• The whole part is responsible for creation and
destruction of its parts.
RootSystem
Plant
Stem
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Specialization/Generalization
• 具体化/概括化
• It is a “is a ” relationship
• For example:
– Client is a person.
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Specialization/Generalization notation
• Specialization/generalization is represented in
UML by adding a triangle next to the
generalization class:
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Specialization/Generalization (cont.)
• How do we structure these classes?
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Specialization/Generalization (cont.)
• Employee and Manager are Person
• Manager is an Employee
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Specialization/Generalization (cont.)
• The associate is a inheritance relationship.
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Specialization/Generalization (end)
• A subclass inherits from its superclass:
– Attributes
– Operations
– Relationships.
• A subclass may add to its definition:
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Attributes
Operations
Relationships
Redefine inherited operations
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Common Class Structure
• Although the definition of classes and their relationships
depends on the particular application, some class
structures are common to many designs.
• These class structures are thought of as basic building
blocks and can be composed to design complex systems.
• Some of common class structure:
– Collection(集合)
– Self-containing(自容类)
– Relationship loops(关系环)
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Collection
• A collection models a one-to-many relationship.
• Collections store many instances of one class.
• For example:
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Collections
• 在该类中有一个属性是BankAccout类的实例集合；
• 每个BankAccout类的实例都有一个索引值；
• 该类中提供了增加和获取BankAccout类的实例的方法；
集合
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Self-containing
• A class can have an association with itself.
• 一个类有一个与其自身的关联，即该类包含一
个同类对象的引用作为其属性；
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Self-Containing Classes
• The following diagram shows the relationship
"each employee has one boss."
• The diagram indicates that the boss of an
employee is another employee.
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Relationship Loops
• Self-containment can be found in relationships that
include two or more classes
– 在多个类之间存在自容关系，就会形成关系环。
• An example of a self-containment loop is a file
system.
– A file system has folders, and folders contain files or
more folders, or both
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Class Diagram of a Files System
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Roundup: Class Diagrams
• Class Diagrams …
– show a set of classes and their relationships to each
other.
– illustrate the static view of a system.
– are different from “object diagrams”.
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UML Class Diagram Tools
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Eclipse
PPT
Microsoft Visio
Violet
IBM Rational Rose
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UML with eclipse
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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
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