An Introductory session of Design Patterns.

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2. What is Design Pattern
Design pattern is a general reusable
solution to a commonly occurring
problem in software design.
A design pattern is not a finished
design that can be transformed
directly into code. It is a description
or template for how to solve a
problem that can be used in many
different situations.
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4. History
Civil Engineer
Christopher Alexander.
Gang of four : Erich Gamma, Richard Helm,
Ralph Johnson, and John Vlissides
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5. Why Design Patterns
• To design a new software system quickly and
efficiently.
• To understand a existing software system.
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6. Types of Design Pattern
• Creational Design pattern
– Object creation.
• Structural design patterns
– Relationship between entities.
• Behavioural design patterns
– Communication between objects.
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7. Observer Design Pattern
• Observer Design Pattern is a software design
pattern in which an object, called the subject,
maintains a list of its dependents, called
observers, and notifies them automatically of
any state changes, usually by calling one of
their methods.
• Type : Behavioral pattern.
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8. Factory Design Pattern
• Define an interface for creating an object, but
let the subclasses decide which class to
instantiate. The Factory method lets a class
defer instantiation to subclasses.
• Type : Creational pattern.
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9. Singleton Design Pattern
• Ensure a class has only one instance, and
provide a global point of access to it.
• Encapsulated “just-in-time initialization” or
“initialization on first use”.
• Type : Creational pattern.
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10. UML Diagram for Singleton
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11. Strategy Design pattern
The strategy pattern (also known as the policy
pattern) is a particular software design pattern,
whereby algorithms can be selected at runtime.
Type : Behavioral pattern.
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12. Adaptor Design pattern
The adapter pattern (often referred to as the
wrapper pattern or simply a wrapper) is a
design pattern that translates one interface
for a class into a compatible interface.
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13. Proxy Design Pattern
A proxy, in its most general form, is a class
functioning as an interface to something else.
The proxy could interface to anything: a
network connection, a large object in memory,
a file, or some other resource that is
expensive or impossible to duplicate.
Type : Structural pattern.
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14. Chain of responsibilities
The chain-of-responsibility pattern is a design
pattern consisting of a source of command objects
and a series of processing objects. Each processing
object contains a set of logic that describes the types
of command objects that it can handle and how to
pass off those that it cannot to the next processing
object in the chain
Type : Behavioral pattern.
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15. Decorator Design pattern
The decorator pattern is a design pattern that
allows new/additional behaviour to be added
to an existing object dynamically.
Type: Structural patterns
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16. Template method pattern
A template method defines the program
skeleton of an algorithm. One or more of the
algorithm steps are able to be overridden by
subclasses to provide their own concrete
implementation.
Type : Behavioral Design Pattern.
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17. Builder pattern
The intention is to abstract steps of
construction of objects so that different
implementations of these steps can construct
different representations of objects.
Type : Creational Design Pattern.
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18. Façade pattern
A facade is an object that provides a
simplified interface to a larger body of code,
such as a class library.
Type: Structural Design Pattern.
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19. Iterator pattern
The Iterator pattern is a design pattern in
which iterators are used to access the
elements of an aggregate object sequentially
without exposing its underlying
representation.
An Iterator object encapsulates the internal
structure of how the iteration occurs.
Type : Behavioral Design Pattern.
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20. Mediator Pattern
• Behavioural pattern
• Definition
– With the mediator pattern communication
between objects is encapsulated with a mediator
object. Objects no longer communicate directly
with each other , but instead communicate
through the mediator . This results in a more
cohesive implementation of the logic and
decreased coupling between the other objects.
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21. Flyweight Pattern
• Structural Pattern
• Definition
– The Flyweight pattern provides a mechanism by
which you can avoid creating a large number of
'expensive' objects and instead reuse existing
instances to represent new ones.
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22. Prototype pattern
• Creational pattern.
• Definition
– The Prototype pattern is basically the creation of
new instances through cloning existing instances.
By creating a prototype, new objects are created
by copying this prototype.
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23. State Pattern
• Behavioral patterns
• Definition
– The State pattern allows an object to alter its
behaviour when its internal state changes. By
using inheritance and letting subclasses represent
different states and functionality we can switch
during runtime. This is a clean way for an object to
partially change its type at runtime.
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24. Thank you…..
• Good read about Design Patterns
– http://en.wikipedia.org/wiki/Design_pattern_(computer_science)
– http://sourcemaking.com/design_patterns
– http://java.sun.com/blueprints/patterns/index.html
– http://www.codeproject.com/KB/architecture/#Design Patterns
– http://msdn.microsoft.com/en-us/magazine/cc301852.aspx
– http://www.javacamp.org/designPattern/
– http://www.javaworld.com/channel_content/jw-patterns-index.html
– http://www.ibm.com/developerworks/java/tutorials/j-patterns201/
• About me
– Email: chetangole@gmail.com
– Web : chetangole.com
If this presentation contains your copyrighted material please contact me at : chetangole@gmail.com
This presentation is the intellectual property of Infospectrum India Private Limited. Any unauthorized use, dissemination of
Infosp ctrum the information, or copying of this presentation, in whole or in part, without the express written permission of Infospectrum
India Private Limited is prohibited. Please send an email to info@info-spectrum.com to obtain written authorization
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