The document discusses UML class diagrams and their components. It defines a class diagram as representing entities with common features as rectangles divided into compartments for the class name, attributes, and operations. It provides examples of how different relationships like association, aggregation, and generalization are depicted. Key points include that association represents a "has-a" relationship, aggregation a whole-part relationship where parts can exist independently, and generalization an "is-a" relationship of inheritance.

1. Software Engineering Principles
Ajit K Nayak, Ph.D.
ajitnayak@soauniversity.ac.in
UML Class Diagram

2. Acknowledgements
• Slides of Prof. Rajib Mall, IIT, KGP

3. Class Diagram
• Entities with common features, i.e.
attributes and operations.
• Represented as solid outline rectangle
with compartments for name, attributes,
and operations.
• Attribute and operation compartments
are optional depending on the purpose of
a diagram.
Window
size: Size
visibility: boolean
display()
hide()
• Java Syntax UML Syntax
• Date birthday Birthday:Date
• Public int duration = 100 +duration:int = 100
• Private Student students[MAX_Size]
Students[MAX_Size]:Student

4. Example: Class Diagram
LibraryMember
Member Name
Membership Number
Address
Phone Number
E-Mail Address
Membership Admission Date
Membership Expiry Date
Books Issued
issueBook( );
findPendingBooks( );
findOverdueBooks( );
returnBook( );
findMembershipDetails( );
LibraryMember
issueBook( );
findPendingBooks( );
findOverdueBooks( );
returnBook( );
findMembershipDetails( );
LibraryMember
Different representations of the
LibraryMember class

5. Visibility
Visibilty Java Syntax UML Syntax
public public +
protected protected #
package ~
private private -

6. Relationships Between Classes
• Association
– Permanent, structural, “has a”
– Solid line (arrowhead optional)
• Aggregation
– Permanent, structural, a whole created from parts
– Solid line with hollow diamond from whole
• Composition
– Whole part relationship (solely owns the part)
– Solid line with solid diamond from whole
• Dependency
– Temporary, “uses a”
– Dotted line with arrowhead
• Generalization
– Inheritance, “is a”
– Solid line with open (triangular) arrowhead
• Implementation
– Dotted line with open (triangular) arrowhead
OR

7. Class Relationships
Relation
AssociationGeneralization Dependency
Aggregation
Binary Association N-ary Association
Composition

8. Association
• Denotes permanent, structural relationship
• State of class A contains class B
• Represented by solid line (arrowhead optional)
• Example: Car and Engine classes know about each other

9. Associations with Navigation Information
• Can indicate direction of relationship
• Represented by solid line with arrowhead
• Gas Pedal class knows about Engine class.
• Engine class doesn’t know about Gas Pedal class
• “Gas Pedal “has an” Engine
• State of Gas Pedal class contains instance of Engine class  can
invoke its methods

10. 1-1 Association – example
People
Rakesh Shukla
V. Ramesh
Tax_files
760901-1234
691205-5678
tax_file
People Tax_files
1 1
Associated with

11. Multiple Association – example
Kunti
Women People
Bhim
Arjun
Yudhistir
Women People
1 *
Mother of
motherOf

12. UML Syntax: Association
• A Person works for a Company.
works for
Person Companyemployee employer
Association Name
Role
Member Book1 0..5borrowed
Lion Animal**
eats
Class A Class B
role A
role B

13. Example 1: Association
• A teacher teaches 1 to 3 courses (subjects)
• Each course is taught by only one teacher.
• A student can take between 1 to 5 courses.
• A course can have 10 to 300 students.
Teacher Course
teaches 1..31
Students takes
1..5
10..300

14. Example 2: Association
• A Student can take up to five Courses.
• A student has to enroll in at least one course.
• Up to 300 students can enroll in a course.
• A class should have at least 10 students.
Student Coursecredits
10..300
1..5
hasEnrolmentOf
Enrols in
Student Course
credits
10..300 1..5
hasEnrolmentOf
Enrols in
Student Coursecredits
10..300 1..5
hasEnrolmentOf
Enrols in

15. Recursive/Reflexive Association
• A class is associated with itself
Person Friend of
Computer
Connects to
*
*
LinkedListNode
next
previous

16. Implementation of Association
• Java Implementation
– Use a reference variable
of one class as an
attribute of another class
Member Book
1 1Borrowed
by
aBook
bookName: OOSD
author: Gamaa
ISBN: 12234434Book Reference
Book instance
bookName:
memberName: AKK
memberNumber: 412323
• Member Class
public class Member{
private Book book;
public issueBook(Book aBook){
setBook(aBook);
abook.setLender(this);}
setBook(Book aBook){
book=aBook; }
…}//end class

17. Implementation contd.
• Java Implementation
– Use a reference variable
of one class as an
attribute of another class
Member Book
1 1Borrowed
by
abook
bookName: OOSD
author: Gamaa
ISBN: 12234434Book Reference
Book instance
bookName:
memberName: AKK
memberNumber: 412323
• Book Class
public class Book{
private Member member;
setLender(Member aLender){
member=aLender;
}
…
}//end class

18. Implementation Example 2
• Java Code
class Customer{
private ArrayList <Account> accounts =
new ArrayList<Account>();
public Customer(){
Account defaultAccount = new
Account();
accounts.add(defaultAccount);
}
}
Customer Account
1..*1
has

19. Ternary Association
• Decompose it to a set of
binary associations
Man Woman
1 1
Priest
1..3
Man Woman
Priest
Performed by
1 1
1..3
Marriage
Participates
in
1 1
Participates
in*

20. Aggregation
• A special kind of association
• Models whole-part relationship
between things
• Whole is usually referred to as
composite
• the child can exist independently of the
parent.
• Composition
– child cannot exist independent of the
parent
Library
Books
1 0..7
Hand Finger

21. Aggregation Implementation
public class Car{
private Wheel wheels[4];
public Car (Wheel w[4]){
wheels[0] = w[0];
wheels[1] = w[1];
wheels[2] = w[2];
wheels[3] = w[3];
}
}
Car Wheel1 4

22. Composition Implementation
public class Car{
private Wheel wheels[4];
public Car (){
wheels[0] = new Wheel();
wheels[1] = new Wheel();
wheels[2] = new Wheel();
wheels[3] = new Wheel();
}
}
Car Wheel1 4

23. Dependency
• Denotes dependence between
classes
• Always directed (Class A depends
on B)
A B
• Represented by dotted line with arrowhead
• Caused by class methods
– Method in Class A temporarily “uses a” object of
type Class B
– Change in Class B may affect class A
• Dependence may be caused by
– Local variable
– Parameter
– Return value
class A {
B Foo(B x) {
B y = new B();
return y;
}
}

24. Generalization
• Denotes inheritance between classes
• Can view as “is-a” relationship
• Represented by line ending in (open) triangle
Laptop, Desktop, PDA inherit state & behavior
from Computers

25. Implementation
• Denotes class implements Java interface
• Represented by dotted line ending in (open) triangle
A implements interface B
A «B»

26. UML Example – I
• Read the UML Diagrams
– 1 or more Pets associated with 1 PetOwner
– 1 CPU associated with 0 or more Controllers
– 1-4 DiskDrives associated with 1 SCSIController
– SCSIController is a (specialized) Controller

27. UML Example – II
• 1 Bank associated with 0 or more Accounts
• Checking, Savings, MoneyMarket are Accounts

28. Example - III
• Each Thermostat has 1 Room
• Each Thermostat associated with 0 or more
Heaters
• ElectricHeater is a specialized Heater
• AubeTH101D is a specialized Thermostat

29. Draw class diagram of A Web Browser
• The user can enter a URL and as a result, the
corresponding file is fetched and its contents is displayed
in the main window.
• At each moment in time, only one file is open, whose URL
is written in the status bar.
• There are two types of files, HTML files and image files;
each type has its own display method.
• An HTML file may in turn have references to image files.
• The display method of both types of files takes a canvas to
draw the contents on it, and when the browser wants to
display a file, the canvas is the main window of the
browser.
• There is a “home” button on the browser, which takes the
browser to a pre-set URL. The “home” URL can be set at
any time by the user.

30. Class diagram of the WEB BROWSER

31. Thank You