[Tutorial] Design Pattern – Factory Pattern

 “Creates an instance of several families of classes”

Rules of thumb

• Abstract Factory classes are often implemented with Factory Methods, but they can be implemented using Prototype.
• Factory Methods are usually called within Template Methods.
• Factory Method: creation through inheritance. Prototype: creation through delegation.
• Often, designs start out using Factory Method (less complicated, more customizable, subclasses proliferate) and evolve toward AbstractFactory, Prototype, or Builder (more flexible, more complex) as the designer discovers where more flexibility is needed.
• Prototype doesn’t require subclassing, but it does require an Initialize operation. Factory Method requires subclassing, but doesn’t require Initialize.
• The advantage of a Factory Method is that it can return the same instance multiple times, or can return a subclass rather than an object of that exact type.
• Some Factory Method advocates recommend that as a matter of language design (or failing that, as a matter of style) absolutely all constructors should be private or protected. It’s no one else’s business whether a class manufactures a new object or recycles an old one.
• The new operator considered harmful. There is a difference between requesting an object and creating one. The newoperator always creates an object, and fails to encapsulate object creation. A Factory Method enforces that encapsulation, and allows an object to be requested without inextricable coupling to the act of creation.

Download full source code here

Tại đây, công ty MegaGigaCo, bạn được trả lương cao cho kỹ năng thiết kế mẫu chuyên nghiệp của mình, bạn đang tạo một đối tượng kết nối cơ sở dữ liệu mới

cConnection conn = new cOracleConnection();

cConnection conn = new cSqlServerConnecton();

“Tốt lắm” Vị giám đốc nói. “Umh, vậy làm sao để kết nối với MySQL? Chúng ta muốn nó là kết nối mặc định”. “Woa”, bạn hơi bối rối. Tuy nhiên bạn vẫn làm thêm một kết nối với MySQL như sau:

cConnection conn = new cMySqlServerConnecton();

Hiện tại bạn đã có ba loại kết nối cơ sở dữ liệu như sau: Oracle, SQL Server và MySQL. Vì vậy bạn chỉnh sửa mã nguồn cho phù hợp với các biến như “Oracle”, “SQL Server” hay bất cứ biến nào khác như sau:

if (type.equals("Oracle"))
    conn = new cOracleConnection();
    

else if (type.equals("SQL Server"))
    conn = new cSqlServeverConnection();    

else
    conn = new cMySqlServerConnection(); 

1st Exam:

abstract class Address
{
    public abstract void Show();
}

abstract class Phone
{
 public abstract void Show();
}

abstract class Factory
{
 virtual public Address createAddress()
 {
  return null;
 }
 virtual public Phone createPhone()
 {
  return null;
 }
}

class USAddress: Address
{
 public override void Show()
 {
  Console.WriteLine("USA Address");
 }
}

class USPhone: Phone
{
 public override void Show()
 {
  Console.WriteLine("USA Phone");
 }
}

class VNAddress: Address
{
 public override void Show()
 {
  Console.WriteLine("Viet Nam address");
 }
}

class VNPhone:Phone
{
 public override void Show()
 {
  Console.WriteLine("Viet Nam phone");
 }
}

class USFactory: Factory
{
 public override Address createAddress()
 {
  return new USAddress();
 }
 public override Phone createPhone()
 {
  return new USPhone();
 }
}

class VNFactory:Factory
{
 public override Address createAddress()
 {
  return new VNAddress();
 }
 public override Phone createPhone()
 {
  return new VNPhone();
 }
}

class Program
{
 static void Main(string[] args)
 {
  Factory factory = new VNFactory();
  Address address = factory.createAddress();
  Phone phone = factory.createPhone();
    
  Console.WriteLine("Create Object by VNFactory");
  address.Show();
  phone.Show();

  factory = new USFactory();
  address = factory.createAddress();
  phone = factory.createPhone();

  Console.WriteLine("Create Object by USFactory");
  address.Show();
  phone.Show();

  Console.ReadKey();
 }
}

2nd Exam:

Ref:
https://sourcemaking.com/design_patterns/factory_method
https://haihth.wordpress.com/2013/02/21/dp-chapter3/