[designmode] factory pattern

1. Simple factory model

1. The simple factory pattern is a creation pattern , It's a kind of factory model . The simple factory pattern is that a factory object determines which product to create
   Class . The simple factory pattern is the simplest and most practical pattern in the family of factory patterns

2. Simple factory model ： Defines a class for creating objects , This class encapsulates the behavior of the instantiated object ( Code )

3. In software development , When we're going to use a lot to create a certain 、 When a class or a batch of objects , It will use the factory mode .

1.1 Look at a specific need

Look at a pizza project ： To facilitate the expansion of pizza varieties , Be easy to maintain

1. There are many kinds of pizza ( such as GreekPizz、CheesePizz etc. )

2. Pizza is made of prepare,bake, cut, box

3. Complete the pizza order function .

1.2 Use the traditional way to complete

Class diagram ：

Code :

//public class OrderPizza { 
    
//  Constructors 
// public OrderPizza() { 
    
// Pizza pizza = null;
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