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Factory model

Factory pattern is a creative pattern pattern that solves some problems in new objects, such as dependency, coupling, post-maintenance, etc.

1. Simple factory model

For example, there is a pizza restaurant. The process of making pizza is as follows. New the pizza directly in the code, and then do some operations, as follows:

We encapsulate the new code and move it to a separate class (SimplePizzaFactory). Our new class is the factory, as follows

The final code is as follows

Summary:

The new SimplePizzaFactory is a simple factory pattern (generally, there are no subclasses and no inheritance relationships). Let's take a look at the definition as follows:

two。 Factory method model

Definition: define an interface for creating objects, let subclasses decide which class to instantiate, and factory methods defer the instantiation of a class to its subclasses.

Question: if there are two branches in the pizza parlor, one in the United States and the other in English, then they need to produce localized pizzas. It is time to introduce the factory method model. The class diagram is as follows:

Description: the pizzaStore superclass (factory class) has two subclasses, each of which determines which products to instantiate.

3. Abstract factory pattern

Definition: the abstract factory pattern provides an interface for creating families of related or dependent objects without explicitly specifying concrete classes. It can be understood as a combination of multiple factory methods.

Solve the problem: in the factory method pattern, our specific creator can only create one object of the same type at a time, and if we need multiple different types of objects now, the factory method will not meet the requirements. At this point, we can combine multiple factory methods into one class, which is the abstract factory pattern, which is specifically used to create multiple products, or to create product families. The class diagram is as follows:

Demand: in order to ensure quality, when we need to unify the raw materials, it is suitable for abstract factories to solve. The class diagram is as follows:

Advantages of Abstract Factory pattern

(1) allow customers to create a set of related products using abstract interfaces without knowing (or caring about) what specific products are produced, so that customers can be decoupled from specific products.

(2) A specific factory can create multiple products, which can generate fewer classes of a specific factory than the factory method pattern.

(3) easy to exchange product series, as long as the specific factory can be changed, this product series can be changed.

Abstract factory pattern and its disadvantages

(1), abstract factory is the use of a combination of factory methods into a class, when adding a product family member, it is necessary to modify the abstract factory class and the following specific factory class, so its scalability is poor.

(2) each new product subclass has to create a class, when there are too many product subclasses, there will be many classes, resulting in increased complexity of the system.

The use of abstract factory patterns

1. Use it when you need to create a product family, or when you want to bring the created products together.

2. When the series of products is not fixed, it may be used when the whole series of products may be added in the future.

Design principles:

1. Open for extensions and closed for modifications.

two。 Rely on abstractions, not concrete classes.

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