The document provides an overview of class diagrams in object-oriented analysis and design. It discusses that class diagrams describe the static view of a system by showing classes, interfaces, associations, and constraints. Class diagrams represent the attributes and operations of classes and can be mapped directly to object-oriented languages. The purpose of class diagrams is to analyze and design the static view of an application and describe its responsibilities. Elements and relationships in class diagrams should be clearly identified and minimum properties specified to avoid complexity.

1. Object Oriented Analysis &
Design
Lecture 16
Class Diagrams
Sajiya Tariq

2. Overview
•The class diagram is a static diagram. It
represents the static view of an application.
•The class diagram describes the attributes and
operations of a class and also the constraints
imposed on the system.
•The only UML diagrams which can be mapped
directly with object oriented languages.
•The class diagram shows a collection of classes,
interfaces, associations, collaborations and
constraints. It is also known as a structural
diagram.
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3. Purpose
The purpose of the class diagram can be
summarized as:
•Analysis and design of the static view of
an application.
•Describe responsibilities of a system.
•Base for component and deployment
diagrams.
•Forward and reverse engineering.
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4. Points to remember
• The name of the class diagram should be meaningful to
describe the aspect of the system.
• Each element and their relationships should be identified in
advance.
• Responsibility (attributes and methods) of each class should
be clearly identified.
• For each class minimum number of properties should be
specified. Because unnecessary properties will make the
diagram complicated.
• Use notes when ever required to describe some aspect of
the diagram. Because at the end of the drawing it should be
understandable to the developer/coder.
• Finally, before making the final version, the diagram should
be drawn on plain paper and rework as many times as
possible to make it correct.
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5. UML Class Diagram
• What is a UML class diagram?
▫ UML class diagram: a picture of
▫ the classes in an OO system
▫ their fields and methods
▫ connections between the classes that interact or inherit from
each other
• What are some things that are not represented in a UML
class diagram?
▫ details of how the classes interact with each other
▫ algorithmic details; how a particular behavior is
▫ implemented
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6. Diagram of one Class
• class name in top of box
▫ write <<interface>> on top of
interfaces' names
▫ use italics for an abstract class
name
• Attributes (optional)
▫ should include all fields of the
object
• Operations / methods (optional)
▫ may omit trivial (get/set) methods
 but don't omit any methods from an
interface!
▫ should not include inherited
methods
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7. Class Attributes
• attributes (fields, instance variables)
▫ visibility name : type [count] =
default_value
▫ visibility: + public
# protected
- private
~ package (default)
/ derived
▫ underline static attributes
▫ derived attribute: not stored, but can be
computed from other attribute values
▫ attribute example:
 balance : - = double 0.00
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8. Class Operations and Methods
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9. Comments
• represented as a folded note, attached to the
appropriate class/method/etc by a dashed line
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10. Relationships btwn. classes
•generalization: an inheritance
relationship
▫inheritance between classes
▫interface implementation
•association: a usage relationship
▫dependency
▫aggregation
▫composition
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11. Generalization Relationship
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12. Associational Relationship
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13. Multiplicity of associations
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14. Association types
• aggregation: "is part of"
▫ symbolized by a clear white
diamond
• composition: "is entirely made of"
▫ stronger version of aggregation
▫ the parts live and die with the
whole
▫ symbolized by a black diamond
• dependency: "uses temporarily"
▫ symbolized by dotted line
▫ often is an implementation detail,
not an intrinsic part of that
object's state
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15. Composition/aggregation
example
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16. Class diagram example:Video
Store
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