Lecture-7.pptx software design and Arthitechure

Lecture 07
Software Design
Patterns
Software Design &
Architecture

Patterns and Software Design Patterns
• Design Patterns
• Uses of Design Patterns
• Types of Software Design Pattern
1. Creational Design Patterns
2. Structural Design Patterns
3. Behavioral Design Patterns
2

Design Pattern
Design patterns are evolved as reusable solutions to the problems
that we encounter everyday of programming.
3

Uses of Design
Pattern
1. Speed up the development/implementation process (To
support reuse in design and boost confidence in software
systems.)  Reuse Solution
2. To provide a common vocabulary for software designers to
communicate their designs  Shared Vocabulary
4

Uses of Design
Pattern
3. Design patterns provide you not with
code reuse but with experience reuse
– Knowing concepts such as abstraction, inheritance and
polymorphism will NOT make you a good designer, unless you
use those concepts to create flexible designs that are
maintainable and that can cope with change
5

What is a
Pattern
?
“A pattern describes a problem that occurs often, along with
a tried solution to the problem”
- Christopher Alexander, 1977
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What is a Design
Pattern
?
• Design patterns are descriptions of communicating objects
and classes that are customized to solve a general design
problem in a particular context.
• A design
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pattern isn't 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.

Elements of Design Pattern
• In general, a pattern has four essential elements:
1. Pattern Name- Useful part of software design
2. Problem- When to apply the pattern
3. Solution- Elements that make up the pattern,
their relationships, responsibilities, and collaborations.
4. Consequences- Results and trade-offs of applying the pattern
8

Types of Design Patterns
1. Creational patterns
– Creating a collection of objects in flexible ways
2. Structural patterns
– Representing a collection of related objects
3. Behavioral patterns
– Capturing behavior among a collection of
objects.
9

Creational Design Pattern
• In software engineering, creational design patterns are design
patterns that deal with object creation mechanisms, trying to
create objects in a manner suitable to the situation.
• The basic form of object creation could result in design
problems or added complexity to the design. Creational design
patterns solve this problem by somehow controlling this
object creation
10

Creational Design Pattern
• Factory
• Singleton
• Abstract Factory
• Prototype
11

Factory: Creational Design Pattern
• Design Purpose
Create individual objects in situations where the
constructor alone is inadequate.
• Design Pattern Summary
Use methods to return required objects.
In class-based programming, the factory method pattern is a
creational pattern that uses factory methods to deal with the problem of
creating objects without having to specify the exact class of the object
that will be created.
12

Factory: Example
• Motive: Use Factory when a base class object is required but
the subclass to which it belongs is not known until runtime.
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Creational Design Pattern (Cont...)
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• Factory
• Singleton
• Prototype
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Singleton Design Pattern
•
Design Purpose
Ensure a class (e.g S) has only one instance , and provide a
global point of access to it
.
•
Design Pattern Summary
Make the constructor of S private; define a private static
attribute for Singleton class of type S; define a public accessor
for it
.
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The Singleton Design Pattern Applied to
MyClass: 3 Steps
1. Define a private static member variable of MyClass of type
MyClass
private static MyClass singletonOfMyClass = new MyClass();
2. Make the constructor of MyClass private
private MyClass() { /* ….constructor code …. */ };
3. Define a public static method to access the member
public static MyClass getSingletonOfMyClass()
{
return singletonOfMyClass;
}
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• Factory
• Singleton
• Prototype
22

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