The document discusses different categories of design patterns including creational, structural, and behavioral patterns. It provides details on the Factory Pattern, including that it is one of the most used patterns in Java to create objects without exposing creation logic. The Factory Pattern allows hiding implementation and easy testing. The document also discusses the Visitor Pattern as a behavioral pattern that operates on two objects based on their type, providing a real-world shopping cart example and explaining how it works and its pros and cons.

1. Design pattern
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2. Design pattern categories
• Creational Patterns
• These design patterns provide a way to create objects while hiding the creation logic,
rather than instantiating objects directly using new opreator. This gives program
more flexibility in deciding which objects need to be created for a given use case.
• Structural Patterns
• These design patterns concern class and object composition. Concept of inheritance
is used to compose interfaces and define ways to compose objects to obtain new
functionalities.
• Behavioral Patterns
• These design patterns are specifically concerned with communication between
objects.
• J2EE Patterns
• These design patterns are specifically concerned with the presentation tier. These
patterns are identified by Sun Java Center.

3. Factory Pattern
• One of most used design pattern in Java
• Create object without exposing the creation logic to the client
and refer to newly created object using a common interface

4. Factory Pattern
• Pros
• Allows you to hide implementation of an application seam (the core interfaces
that make up your application)
• Allows you to easily test the seam of an application (that is to mock/stub)
certain parts of your application so you can build and test the other parts
• Allows you to change the design of your application more readily, this is
known as loose coupling
• Con's
• Makes code more difficult to read as all of your code is behind an abstraction
that may in turn hide abstractions
• Can be classed as an anti-pattern when it is incorrectly used, for example
some people use it to wire up a whole application when using an IOC
container, instead use Dependency Injection.
• Too much abstract 

5. Factory Pattern: Installation
• Procedural Solution - switch/case noob instantiation
• Most simple and intuitive
• Add new concrete product call we should modify the Factory class? ->
not very flexible

6. Factory Pattern: Installation

7. Factory Pattern: Reflection
• Class Registration - reflection

8. Discussion
• Factory Pattern vs Dependency Injection?

9. Visitor Pattern
• What is that?
• Behavior pattern category
• Do the right thing based on the type of two objects
• When: Lets you define a new operation without changing the classes
of the elements on which it operates
• Real world example
• Shopping cart when you shopping in supermarket which include product a,
product b…
• The cashier acts as a visitor, taking the disparate set of elements. Some of
them using prices, some need to be weighted to provide you total

10. Visitor Pattern: How

11. Visitor Pattern: Example

12. Visitor Pattern: Pros & Cons
• PROs
• Allows you to add operations to a Composite structure without changing the
structure itself
• Adding new operations is relatively easy
• The code for operations performed by the Visitor is centralized
• CONs
• Encapsulation is broken when the Visitor is used
• Because the traversal function is involved, changes to the Composite
structure are more difficult