This document discusses the flyweight design pattern. It begins by defining design patterns as reusable solutions to common software design problems. It then defines the flyweight pattern specifically as a structural pattern that reuses similar objects by storing them and creating new objects only when no match is found. Key advantages are reducing the number of objects and memory usage. The flyweight pattern should be used when there are many objects and storage costs are high. It separates object state into intrinsic and extrinsic parts.

1. Fly Weight
Design
Pattern
SAIFULLAH FA20-BSE-102
RASHID FA20-BSE-081

2. Content
What is Design Pattern
What is Flyweight Design Pattern
When should we use the design patterns?
Types of Design Pattern
Flyweight Design Pattern
Advantage of Flyweight Pattern
Usage of Flyweight Pattern
How to Implement
Example

3. What is Design Pattern
A. Design Pattern is a well-proved solution for solving the specific
problem/task.
B. It is a general reusable solution to a commonly occurring problem in
software design.
C. Example.....

4. What is Design Pattern
A. A design pattern isn't a finished design that can be transformed
directly into code.
B. It is a description or template for how to solve a problem that can
be used in many different situations.

5. When should we use the design
patterns?
We must use the design patterns during the analysis and
requirement phase of SDLC(Software Development Life
Cycle).

6. Types of Design Pattern
1. Creational
2. Structural
3. Behavioral

7. Flyweight
Design Pattern
1. It is a structural design
Pattern
2. Flyweight pattern is primarily
used to reuse already
existing similar kind of
objects by storing them and
create new object when no
matching object is found:

8. Advantage of Flyweight Pattern
1. It reduces the number of objects.
2. It reduces the amount of memory and storage devices required if the objects
are persisted

9. Usage of Flyweight Pattern
1. When an application uses number of objects
2. When the storage cost is high because of the quantity of objects.
3. When the application does not depend on object identity.

10. How to Implement
1.Divide fields of a class that will become a
flyweight into two parts:
1. The intrinsic state: the fields that contain unchanging data
duplicated across many objects
2. The extrinsic state: the fields that contain contextual data
unique to each object

11. How to Implement
2. Leave the fields that represent the intrinsic state in the class
3. Go over methods that use fields of the extrinsic state. For
each field used in the method, introduce a new parameter and
use it instead of the field.

12. Real world example of flyweight pattern
1. Suppose we have a pen which can exist with/without refill.
2. A refill can be of any color thus a pen can be used to create drawings
having N number of colors.
3. Here Pen can be flyweight object with refill as extrinsic attribute.
4. All other attributes such as pen body, pointer etc. can be intrinsic
attributes which will be common to all pens.
5. A pen will be distinguished by its refill color only, nothing else.

13. Real world example of flyweight pattern
All application modules which need to access a red pen – can use the
same instance of red pen (shared object). Only when a different
color pen is needed, application module will ask for another pen
from flyweight factory.

14. Thank You……