Transcript COS240Lec52_OOModelingAndDesign

COS240 O-O Languages
AUBG, COS dept
Lecture 52
Title:
OO Modeling & OO Design
(to model the application in terms of
cooperative objects)
Reference: COS240 Syllabus
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Motivations
The Java/C# lectures introduced objects, classes, class
inheritance, interfaces, polymorphism, EH and EvH, i.e.
Java and C# as OOPL.
 You learned the concepts of OOP.
 This lecture focuses on the analysis and design of
software systems using the OO approach.
 You will learn class-design guidelines, and the
techniques and patterns for designing reusable classes.

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Lecture contents:








To become familiar with the process of program development.
To learn the relationship types: association, aggregation, composition,
dependency, strong inheritance, and weak inheritance.
To discover classes and determine responsibilities of each class.
To declare classes to represent the relationships among them.
To design systems by identifying the classes and discovering the
relationships among these classes.
To implement the Rational class and process rational numbers using this
class.
To design classes that follow the class-design guidelines.
To introduce design patterns for developing sound software systems.
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Software Development Process
 SDP
= SDM = PDM, also
 Software Life Cycle
 There exist various models of SWLC
– Build and Fix model
– Waterfall model – see next slide(s).
– Rapid Prototyping model
– Spiral model
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Software Development Process
Requirement
Specification
System
Analysis
System
Design
Implementation
Testing
Deployment
Maintenance
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Requirement Specification
A formal process that seeks to understand
the problem and document in detail what
the software system needs to do.
This phase involves close interaction
between users and designers.
Requirement
Specification
System
Analysis
System
Design
Implementation
Most of the examples in COS240 are simple,
and their requirements are clearly stated. In
the real world, however, problems are not
well defined. You need to study a
Testing
Deployment
problem carefully to identify its
requirements.
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Maintenance
6
System Analysis
Seeks to analyze the business
process in terms of data flow, and
to identify the system’s input and
output.
Requirement
Specification
System
Analysis
System
Design
Implementation
Part of the analysis entails
modeling the system’s behavior.
The model is intended to capture the
essential elements of the system and
to define services to the system.
Testing
Deployment
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Maintenance
7
System Design
The process of designing the
system’s components.
Requirement
Specification
System
Analysis
System
Design
Implementation
This phase involves the use of many levels
of abstraction to decompose the problem
into manageable components, identify
classes and interfaces, and establish
relationships among the classes and
interfaces.
Testing
Deployment
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Maintenance
8
Implementation
Requirement
Specification
System
Analysis
System
Design
The process of translating the
system design into programs.
Separate programs are written for
each component and put to work
together.
Implementation
This phase requires the use of a
programming language like Java or
C#.
The implementation involves
coding, testing, and debugging.
Testing
Deployment
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Maintenance
9
Testing
Requirement
Specification
Ensures that the code meets the
requirements specification and
weeds out bugs.
System
Analysis
System
Design
Implementation
An independent team of software
engineers not involved in the
design and implementation of the
project usually conducts such
testing.
Testing
Deployment
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rights reserved. 0132130807
Maintenance
10
Deployment
Requirement
Specification
Deployment makes the project
available for use.
System
Analysis
System
Design
Implementation
For a Java applet, this means
installing it on a Web server; for a
Java application, installing it on the
client's computer.
Testing
Deployment
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rights reserved. 0132130807
Maintenance
11
Maintenance
Requirement
Specification
Maintenance is concerned with
changing and improving the
product.
System
Analysis
System
Design
Implementation
Testing
A software product must continue to
perform and improve in a changing
environment. This requires periodic
upgrades of the product to fix newly
discovered bugs and incorporate changes.
Deployment
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Maintenance
12
Discovering Classes
One popular way for facilitating the discovery process is by
creating CRC cards. CRC stands for classes, responsibilities,
and collaborators. Use an index card for each class, as shown
in the Figure below.
Class name
Student
Register a course
Course
Responsibilities
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Collaborators
13
Discovering Class Relationships
 Association
 Aggregation
and Composition
 Dependency
 Inheritance
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Association
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Association
Association represents a general binary relationship that describes
an activity between two classes.
Association illustrated using a solid line btw two classes.
Examples:
This is pure naked illustration.
No labels, no directions, no multiplicity, no roles
See next slide – the same association illustrated in more
informative way.
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Association
Association represents a general binary relationship that describes
an activity between two classes.
Student
5..60
Take
* Course
0..3
Teach
1
Teacher
Faculty
Example 1:
“Student taking a course” is an association btw the Student
class and the Course class.
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Association
Association represents a general binary relationship that describes
an activity between two classes.
Student
5..60
Take
* Course
0..3
Teach
1
Teacher
Faculty
Example 2:
“Faculty member teaching a course” is an association btw
the Faculty class and the Course class.
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Association (Label)
Association represents a general binary relationship that describes
an activity between two classes.
Student
5..60
Take
* Course
0..3
Teach
1
Teacher
Faculty
Association illustrated using:
An optional label to describe the relationship.
E.g. label Take for Example 1
E.g. label Teach for Example 2
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Association (Direction)
Association represents a general binary relationship that describes
an activity between two classes.
Student
5..60
Take
* Course
0..3
Teach
1
Teacher
Faculty
Association illustrated using:
An optional small black triangle to indicate the relationship direction.
Student takes a course as opposed to Course taking a student
Or
Faculty teaches a course as opposed to Course teaching faculty.
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Association (Role)
Student
5..60
Take
* Course
0..3
Teach
1
Teacher
Faculty
Association illustrated using:
Each
class involved in the relationship may have a role name that
describes the role played by the class in the relationship. The role
name for Faculty class is: Teacher
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Association (Multiplicity)
Student
5..60
Take
* Course
0..3
Teach
1
Teacher
Faculty
Association illustrated using:
Each
class involved in association may specify a multiplicity, i.e.
number or range interval to specify how many objects of the class are
involved in the relation.
* Means unlimited number of objects; + means 1 or more; m..n
means a range
Each student may take any number of courses (*).
Each course must have at least 5 and at most 60 students (5..60).
Each course is taught by one only faculty (1).
Each faculty may teach from 0 to 3 courses per semester (0..3).
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Association
An association is usually represented as a data field in the class.
Student
5..60
Take
public class Student {
/** Data fields */
private Course[]
courseList;
* Course
0..3
Teach
public class Course {
/** Data fields */
private Student[]
classList;
private Faculty faculty;
/** Constructors */
/** Methods */
/** Constructors */
/** Methods */
}
1
Teacher
Faculty
public class Faculty {
/** Data fields */
private Course[]
courseList;
/** Constructors */
/** Methods */
}
}
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Translation is not Unique
NOTE: If you don’t need to know the courses a
student takes or a faculty teaches, the data field
courseList in Student
or
courseList in Faculty
can be omitted.
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Association Btw Same Class
1
Person
Supervisor
1
Association may exist between objects of the same class. For example, a person
may have a supervisor.
public class Person {
// data fields omitted
private Person supervisor;
// constructor(s) omitted
// method(s) omitted
}
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Association Between Same Class
If a person may have several supervisors, you may use an array to store supervisors.
public class Person {
// data fields omitted
private Person[] supervisors;
// constructor(s) omitted
// method(s) omitted
}
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rights reserved. 0132130807
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Aggregation and Composition
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Aggregation and Composition
Aggregation is a special form of association, which
represents an ownership relationship between two classes.
Aggregation models the has-a relationship. An object
may be owned by several other aggregated objects.
If an object is exclusively owned by an aggregated object,
the relationship between the object and its aggregated
object is referred to as composition.
Composition
Name
Aggregation
Person
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Address
28
Aggregation and Composition
Aggregation illustrated: an empty diamond attached to the
aggregated object.
“a person has an address” is an aggregation btw Person class and
Address class, since the address may be shared by several persons.
Composition illustrated: a filled diamond attached to the aggregated
object.
“a person has a name” is a composition btw Person class and Name
class, since a name is strictly owned by a person
Composition
Name
Aggregation
Person
Address
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rights reserved. 0132130807
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Representing Aggregation in Classes
An aggregation relationship is usually represented as a data
field in the aggregated class.
public class Name {
/** Data fields */
/** Constructors */
/** Methods */
}
public class Person {
/** Data fields */
private Name name;
private Address address;
public class Address {
/** Data fields */
/** Constructors */
/** Methods */
}
/** Constructors */
/** Methods */
}
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rights reserved. 0132130807
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Inner Classes Translation
If Name or Address is used in the Person class only, they can
be declared as an inner class in Person. For example,
public class Person {
private Name name;
private Address address;
...
class Name {
...
}
class Address {
...
}
}
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rights reserved. 0132130807
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Dependency
A dependency describes a relationship between two classes
where one (called client) uses the other (called supplier). In
UML, draw a dashed line with an arrow from the client class
to the supplier class. For example, the ArrayList class uses
Object because you can add objects to an ArrayList. The
relationship between ArrayList and Object and the
relationship between Calendar and Date can be described
using dependency, as shown in Figures below.
ArrayList
Object
Calendar
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Date
32
Dependency vs. Association
Both
association and dependency describe one class as
depending on another.
Association is stronger than dependency.
In association, the state of the object changes when its
associated object changes.
In dependency, the client object and the supplier object are
loosely coupled.
The association relationship is implemented using data fields
and methods. There is a strong connection between two
classes.
The dependency relationship is implemented using methods.
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rights reserved. 0132130807
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Coupling
Dependency, association, aggregation, and
composition all describe coupling relationships
between two classes. The difference is the degree of
coupling with composition being the strongest,
followed by aggregation, association, and
dependency in this order.
coupling increases
dependency, association, aggregation, composition
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rights reserved. 0132130807
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Inheritance
Inheritance models
is-a or
is-a-kind-of or
is-an-extension-of
relationship between two classes.
Inheritance classified:
Strong is-a relationship describes direct inheritance
btw two classes.
Weak is-a relationship describes that a class has
certain properties.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Strong Inheritance Relationship
Strong is-a relationship can be represented
using class inheritance. For example, see below the
relation “a faculty member is a person”
public class Faculty extends Person {
Person
/** Data fields */
/** Constructors */
/** Methods */
Faculty
}
(A)
(B)
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rights reserved. 0132130807
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Weak Inheritance Relationship
A weak is-an-extension-of relationship can be represented
using interfaces. For example, the weak is-an-extension-of
relationship “students are comparable based on their grades” can be
represented by implementing the Comparable interface, as follows:
public class Student extends Person
implements Comparable {
Person
/** Data fields, Constructors, and */
/** Methods */
Student
Comparable
/** Implement the compareTo method */
public int compareTo(Object object) {
// ...
}
}
(A)
(B)
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Thank You
for
Your attention!
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