The document discusses the decorator design pattern. The decorator pattern allows adding new behaviors to existing objects at runtime by placing them inside decorator objects that contain the original object. This allows functionality to be added without changing the object's class. Some key points made are: the decorator pattern adds functionality at runtime through composition; decorations are independent and can be mixed; and it is used to attach additional responsibilities to objects without subclassing. An example using shapes and color decorators is provided to demonstrate implementation.

1. Decorator Pattern
Design Patterns
Tharuka Dilani Siriwardena.
M.A.N.Shahitha Nazrin.
S.P Dimuthu Anuraj.

2. INTRODUCTION

3. DESIGN PATTERNS - DEFINITION
• A general reusable solution to a commonly occurring
problem in software design (Wikipedia).
• It is not a finished design.
• It is a description or template for how to solve a problem
that can be used in many different situations.
• Shows relationship and interactions between classes
and/or objects.

4. DESIGN PATTERNS - CLASSIFICATION
• Creational pattern
• Deal with object creation mechanism
• E.g. Abstract Factory, Singleton
• Structural pattern
• Ease the design by identifying a simple way to realize relationships
between entities
• E.g. Decorator, Proxy
• Behavioral pattern
• Deal with common communication between objects.
• E.g. Chain of Responsibility, Command

5. DESIGN PATTERNS – CLASSIFICATION
Structural Patterns
• 1. Decorator
• 2. Proxy
• 3. Bridge
• 4. Composite
• 5. Flyweight
• 6. Adapter
• 7. Facade
Creational Patterns
• 1. Prototype
• 2. Factory Method
• 3. Singleton
• 4. Abstract Factory
• 5. Builder
Behavioral Patterns
• 1. Strategy
• 2. State
• 3. TemplateMethod
• 4. Chain of
Responsibility
• 5. Command
• 6. Iterator
• 7. Mediator
• 8. Observer
• 9. Visitor
• 10. Interpreter
• 11. Memento

6. Decorator
Structural Design Pattern

7. CONCEPT OF DECORATING IN REAL
WORLD
Before Decorating
After Decorating

8. DEFINITION
• In object-oriented programming, the decorator
pattern is a design pattern that allows new/additional
behaviour to be added to an existing object dynamically.

9. Photo
+
Frame
+
Caption
RAD Family
DECORATOR PATTERN - EXPLAINED

10. • Adds functionality at Runtime.
• The object does not know it is being “decorated”.
• Three is no one big feature-laden class with all the
options in it.
• The decorations are independent of each other.
• The decorations can be composed together in a mix-
and-match fashion.
DECORATOR PATTERN - EXPLAINED

11. IMPLEMENTATION

12. • We're going to create a Shape interface and concrete classes
implementing the Shape interface. We will then create an
abstract decorator class ShapeDecorator implementing the
Shape interface and having Shape object as its instance
variable.
• RedShapeDecorator is concrete class implementing
ShapeDecorator.
• DecoratorPatternDemo, our demo class will use
RedShapeDecorator to decorate Shape objects.

13. DECORATOR PATTERN - UML
DIAGRAM

14. DEMO
Builder Pattern Decorator Pattern

15. • Graphics world (as illustrated).
• I/O namespace of .NET
• System.IO.Stream
• System.IO.BufferedStream
• System.IO.FileStream
• System.IO.MemoryStream
• Cross platform applications (Mobile/Desktop)
• Actual decorator classes in .NET 3.0
• System.Windows.Controls (Base Class)
• Border (Decorator)
• Viewbox (Decorator)
DECORATOR PATTERN – REAL WORLD
SAMPLE

16. • You have:
• An existing component class that may be unavailable for
subclassing.
• You want to:
• Attach additional state or behavior to an object dynamically.
• Make Changes to some objects of a class without affecting
others.
• Avoid subclassing because too many classes could result.
DECORATOR PATTERN – GUIDELINES(1)

17. • But consider using instead:
• The Adapter Pattern
• Sets up an interface between different classes
• The Composite Pattern
• Aggregates an object without also inheriting its interface.
• The Proxy Pattern
• Specifically controls access to objects.
• The Strategy Pattern
• Changes the original object rather than wrapping it.
DECORATOR PATTERN – GUIDELINES(2)

18. BUILDER VS DECORATOR
• Builder patterns makes it easy
to construct an object which
is extensible in independent
directions at construction
time
• Decorator pattern lets you
add extensions to
functionality to an object after
construction time

19. BUILDER VS DECORATOR
• Builder
Elements are must
This acts as a base on top other work
if this fails the object will be incomplete or inconsistent
• Decorator
Elements are optional
This is to add/attach more responsibility to existing
object
This is bonus or extra functionality is won’t affect the
basic behavior

20. Thank You !
ANY QUESTIONS?