1. SOFTWARE DESIGN
PATTERNS
By:-
NANCY GOEL
USN-1MS09IS059
M.S.RAMIAH INSTITUTE OF TECHNOLOGY
INFORMATION SCIENCE AND ENGINEERING
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2. INTRODUCTION
 A design pattern is a descriptions of
communicating objects and classes that are
customized to solve a general design problem in a
particular context.
“Each pattern describes a problem which occurs
over and over again in our environment and then
describes the core of the solution to that
problem, in such a way that you can use this
solution a million times over, without ever doing it
in the same way twice”
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3. CONTD…
 A pattern is a recurring solution to a standard
problem.
 Patterns capture the static and dynamic structure
and collaboration among key participants in software
designs
 A pattern is made by four elements:
• name
• problem
• solution
• consequences
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4. NAME OF DESIGN PATTERN
 Describe a design problems and its solutions in a
word or two.
 Used to talk about design pattern with our
colleagues.
 Used in the documentation.
 Increase our design vocabulary.
 Have to be coherent and evocative.4

5. PROBLEM
 Describes when to apply the patterns.
 Explains the problem and its context.
 Sometimes include a list of conditions that
must be met before it makes sense to apply the
pattern.
 Have to occur over and over again in our
environment.
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6. SOLUTION
 Describes the elements that make up the
design, their relationships, responsibilities and
collaborations.
 Does not describe a concrete design or
implementation.
 Has to be well proven in some projects.
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7. CONSEQUENCES
 Results and trade-offs of applying the pattern.
 Helpful for describe design decisions, for
evaluating design alternatives.
 Benefits of applying a pattern.
 Impacts on a system’s flexibility , extensibility or
portability.
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8. DESCRIPTION OF DESIGN
PATTERN
 Pattern name and classification
 Intent
 Participants
 Collaborations
 Consequences
 Implementation
 Design
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9. TYPES OF PATTERNS
 Creational patterns:
 Abstract the instantiation process
 Make a system independent to its
realization
 Class Creational use inheritance to vary
the instantiated classes
 Object Creational delegate instantiation to
an another object
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10. CONTD…
 Structural patterns:
 Class Structural patterns concern the
aggregation of classes to form largest
structures
 Object Structural pattern concern the
aggregation of objects to form largest
structures
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11. CONTD…
 Behavioral patterns:
 Concern with algorithms and assignment of
responsibilities between objects
 Describe the patterns of communication
between classes or objects
 Behavioral class pattern use inheritance to
distribute behavior between classes
 Behavioral object pattern use object
composition to distribute behavior between
classes 11

12. CREATIONAL PATTERN
 Singleton
 Ensure a class only has one instance
 Provide a global point of access to it
 Abstract Factory
• Provide an interface for creating families
of related or dependent objects without
specifying their concrete classes
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13. CONTD…
 Factory Method
 Define an interface for creating an object
but let subclasses decide which class to
instantiate
 Lets a class defer instantiation to
subclasses
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14. STRUCTURAL PATTERN
 Decorator
 Attach additional responsibilities to an object
dynamically
 Provide a flexible alternative to sub classing for
extending functionality
 Adapter
 Convert the interface of a class into another
interface clients expect
 Lets classes work together that couldn’t
otherwise because of incompatible interfaces 14

15. CONTD…
 Bridge
• Decouple an abstraction from its
implementation so that the two can vary
independently
 Façade
 Provide a unified interface to a set of
interfaces in a subsystem
 Defines an higher-level interface that
makes the system easier to use 15

16. BEHAVIORAL PATTERN
 Observer
 Define a one-to-many dependency
between objects so when one of them
change state all its dependents are
updated automatically
 Strategy
 Define a family of algorithms
 Encapsulate each one
 Make them interchangeable
 Lets the algorithms vary independently
from clients that use it 16

17. DECORATOR PATTERN
 Motivation
 Add responsibilities to individual object
not to an entire class
 conforming the interface of the
component decorated
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18. CONTD...
 Structure Component
Operation()
ConcreteComponent
Operation()
Decorator
Operation()
ConcreteDecoratorA
Operation()
AddedState
ConcreteDecoratorB
Operation()
Addedbehavior 18

19. CONTD…
 Participants
 Component
 Define the interface for objects that can have
responsibilities added to them dinamically
 Concrete Component
 Defines an object to which additional
responsibilities can be attached
 Decorator
 Mantains a reference to a Component object and
defines an interface that conforms to Component’s
interface
 ConcreteDecorator
 Added responsibilities to the component 19

20. CONTD…
 Consequences
 More flexibility than static inheritance
 Avoids feature-laden classes high up in
the hierarchy
 A decorator and its component are not
identical
 Lots of little objects
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21. CONTD…
 Motivation
 If you have a TextView object that
displays text in a Window
 TextView has no scroll bars by default
 TextView has no bord by default …
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22. EXAMPLE
 Structure
VisualComponent
Draw()
TextView
Draw()
Decorator
Draw()
ScrollDecorator BorderDecorator
Draw()
ScrollTo()
ScrollPosition
Draw()
DrawBorder()
BorderWidth
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23. BENEFITS OF DESIGN PATTERNS
 Design patterns enable large-scale reuse of
software architectures and also help document
systems
 Patterns explicitly capture expert knowledge and
design tradeoffs and make it more widely available
 Patterns help improve developer communication
 Pattern names form a common vocabulary
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24. DRAWBACKS TO DESIGN PATTERNS
 Patterns do not lead to direct code reuse
 Patterns are deceptively simple
 Teams may suffer from pattern overload
 Patterns are validated by experience and
discussion rather than by automated testing
 Integrating patterns into a software development
process is a human-intensive activity.
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25. THANK
YOU!!!!!!
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