3. Abstract Factory

3. Abstract factory pattern ( Frequency of use ：*****)

• Factory method model

Each specific factory has only one or a set of overloaded factory methods , Only one product can be produced , It may result in a large number of factory classes in the system , It's bound to increase the overhead of the system

• Abstract factory pattern

A factory can produce a range of products （ A family of products ）, It greatly reduces the number of factories

1. Concept

• Product hierarchy ： Product hierarchy is the inheritance structure of products

• Product family ： Product family refers to the production of , A group of products in a different product hierarchy

• Pattern motivation

When the specific products produced by the factory provided by the system are not a simple object , It's multiple product hierarchies 、 You can use the abstract factory pattern when you belong to different types of concrete products

Abstract factory pattern is the most abstract and general form of factory pattern

• Factory mode definition

Abstract factory pattern ： Provides an interface for creating a series of related or interdependent objects , Without specifying their specific classes . Also known as tools (Kit) Pattern

The concrete factory in the abstract factory pattern is not just to create a product , It's responsible for creating a family of products

When a factory hierarchy can create all objects in a product family that belong to different product hierarchies , Abstract factory pattern is simpler than factory method pattern 、 More efficient

2. Abstract factory pattern structure

The abstract factory pattern includes the following 4 A character ：

1. AbstractFactory（ Abstract factory ）

2. ConcreteFactory（ Specific factory ）

3. AbstractProduct（ Abstract product ）

4. ConcreteProduct（ Specific products ）

3. Abstract factory code implementation

1. Typical abstract factory class code

public interface AbstractFactory {
    
    public AbstractProductA createProductA(); // Factory method one 
    public AbstractProductB createProductB(); // Factory method two 
    ……
}

2. Typical specific factory class code

public class ConcreteFactory1 implements AbstractFactory {
    
    // Factory method one 
    public AbstractProductA createProductA() {
    
        return new ConcreteProductA1();
    }

    // Factory method two 
    public AbstractProductB createProductB() {
    
        return new ConcreteProductB1();
    }
    ……
}

4. Example

A software company wants to develop a set of interface skin library , Can be based on Java Desktop software for interface beautification . The user can select the skin through the menu when using , Different skin will provide different buttons with different visual effects 、 The text box 、 Interface elements such as combo box , For example, spring (Spring) Style skin will provide light green buttons 、 Text box with green border and combo box with green border , And summer (Summer) Style skin offers light blue buttons 、 A text box with a blue border and a combo box with a blue border , Its structure is shown in the following figure

The skin library needs to have good flexibility and scalability , Users can choose different skin freely , Developers can add new skins without modifying existing code .

Now we use the abstract factory pattern to design the interface skin library .

(1) Button： Button interface , Act as an abstract product

(2) SpringButton：Spring Button class , Act as a specific product

(3) SummerButton：Summer Button class , Act as a specific product

(4) TextField： Textbox interface , Act as an abstract product

(5) SpringTextField：Spring Textbox class , Act as a specific product

(6) SummerTextField：Summer Textbox class , Act as a specific product

(7) ComboBox： Combo box interface , Act as an abstract product

(8) SpringComboBox：Spring Combo box class , Act as a specific product

(9) SummerComboBox：Summer Combo box class , Act as a specific product

(10) SkinFactory： Interface skin factory interface , Act as an abstract factory

(11) SpringSkinFactory：Spring Skin factory , Act as a specific factory

(12) SummerSkinFactory：Summer Skin factory , Act as a specific factory

(13) Client： Client test class

Changing the skin only requires changing the configuration file

<?xml version="1.0"?>
<config>
    <className>designpatterns.abstractfactory.SpringSkinFactory
</className>
</config>

5. Expand products

• Add product family ( factory )

  For adding new product families , The abstract factory pattern well supports the open close principle , Just add a specific product and a new specific factory , There is no need to make any changes to the existing code

• Add new product hierarchy

  For adding a new product hierarchy , All factory roles need to be modified , Including abstract factory classes , In all factory classes, we need to add methods to produce new products , Against the principle of opening and closing

6. Advantages and disadvantages

1. advantage

   Isolated the generation of concrete classes , So that the client doesn't need to know what was created

   When multiple objects in a product family are designed to work together , It ensures that clients always use only objects in the same product family

   It's convenient to add new product families , There is no need to modify the existing system , Comply with opening and closing principle

2. shortcoming

   Add new product hierarchy trouble , The original system needs to be greatly modified , You even need to modify the abstract layer code , This will obviously cause great inconvenience , Against the principle of opening and closing

7. Applicable environment of mode

A system should not depend on how product class instances are created 、 The details of composition and expression

There is more than one product family in the system , But use only one product family at a time

Products belonging to the same product family will be used together , This constraint must be reflected in the design of the system

Stable product grade structure , After the design is completed No new product hierarchy will be added to the system or existing product hierarchy will be deleted

Use environment

A system should not depend on how product class instances are created 、 The details of composition and expression

There is more than one product family in the system , But use only one product family at a time

Products belonging to the same product family will be used together , This constraint must be reflected in the design of the system

Stable product grade structure , After the design is completed No new product hierarchy will be added to the system or existing product hierarchy will be deleted