Design Pattern - Factory Method（Java）

阳光穿透心脏的1/2处 2022-05-21 07:47 113阅读 0赞

分享一个大牛的人工智能教程。零基础！通俗易懂！风趣幽默！希望你也加入到人工智能的队伍中来！请点击[http://www.captainbed.net][http_www.captainbed.net]

# Definition #

Define an interface for creating an object, but let sub classes decide which class to instantiate. Factory Method lets a class defer instantiation to sub classes.

# Participants #

The classes and/or objects participating in this pattern are:

*  **Product** **(Page)**
    
     *  Defines the interface of objects the factory method creates
 *  **ConcreteProduct** **(SkillsPage, EducationPage, ExperiencePage)**
    
     *  Implements the Product interface
 *  **Creator** **(Document)**
    
     *  Declares the factory method, which returns an object of type Product. Creator may also define a default implementation of the factory method that returns a default ConcreteProduct object.
     *  May call the factory method to create a Product object
 *  **ConcreteCreator** **(Report, Resume)**
    
     *  Overrides the factory method to return an instance of a ConcreteProduct

# Sample Code in Java #

--------------------

This structural code demonstrates the Factory Method offering great flexibility in creating different objects. The abstract class may provide a default object, but each subclass can instantiate an extended version of the object.

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * A 'ConcreteCreator' class
     *
     * @author Chimomo
     */
    class ConcreteCreatorA extends Creator {
    
        /**
         * Factory method
         *
         * @return The product
         */
        @Override
        public Product factoryMethod() {
            return new ConcreteProductA();
        }
    
    }

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * A 'ConcreteCreator' class
     *
     * @author Chimomo
     */
    class ConcreteCreatorB extends Creator {
    
        /**
         * Factory method
         *
         * @return The product
         */
        @Override
        public Product factoryMethod() {
            return new ConcreteProductB();
        }
    
    }

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class ConcreteProductA extends Product {
    }

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class ConcreteProductB extends Product {
    }

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * The 'Creator' abstract class
     *
     * @author Chimomo
     */
    abstract class Creator {
    
        /**
         * Factory method
         *
         * @return The product
         */
        public abstract Product factoryMethod();
    
    }

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * The 'Product' abstract class
     *
     * @author Chimomo
     */
    abstract class Product {
    }

package chimomo.learning.java.designpattern.factorymethod.sample;
    
    /**
     * Startup class for Structural Factory Method Design Pattern
     *
     * @author Chimomo
     */
    class Program {
    
        /**
         * Entry point into console application
         *
         * @param args The arguments
         */
        public static void main(String[] args) {
    
            // An array of creators
            Creator[] creators = new Creator[2];
            creators[0] = new ConcreteCreatorA();
            creators[1] = new ConcreteCreatorB();
    
            // Iterate over creators and create products
            for (Creator c : creators) {
                Product product = c.factoryMethod();
                System.out.println("Created " + product.getClass().getSimpleName());
            }
        }
    
    }
    
    /* ------ Running Results ------
    Created ConcreteProductA
    Created ConcreteProductB
    
    */

--------------------

This real-world code demonstrates the Factory Method offering flexibility in creating different documents. The derived Document classes Report and Resume instantiate extended versions of the Document class. Here, the Factory Method is called in the constructor of the Document base class.

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class BibliographyPage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class ConclusionPage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * The 'Creator' abstract class
     *
     * @author Chimomo
     */
    abstract class Document {
    
        // The pages
        private final List<Page> pages = new ArrayList<>();
    
        /**
         * Initializes a new instance of the "Document" class. Constructor calls abstract Factory method.
         */
        Document() {
            this.createPages();
        }
    
        /**
         * Create pages
         */
        public abstract void createPages();
    
        /**
         * Get pages
         *
         * @return The pages
         */
        List<Page> getPages() {
            return this.pages;
        }
    
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class EducationPage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class ExperiencePage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class IntroductionPage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * The 'Product' abstract class
     *
     * @author Chimomo
     */
    abstract class Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * Startup class for Real-World Factory Method Design Pattern
     *
     * @author Chimomo
     */
    class Program {
    
        /**
         * Entry point into console application
         *
         * @param args The arguments
         */
        public static void main(String[] args) {
    
            // Note: constructors call Factory Method
            Document[] documents = new Document[2];
            documents[0] = new Resume();
            documents[1] = new Report();
    
            // Display document pages
            for (Document document : documents) {
                System.out.println(document.getClass().getSimpleName() + " ------ ");
                document.getPages().forEach((page) -> System.out.println(page.getClass().getSimpleName()));
            }
        }
    }
    
    /* ------ Running Results ------
    Resume ------
    SkillsPage
    EducationPage
    ExperiencePage
    Report ------
    IntroductionPage
    ResultsPage
    ConclusionPage
    SummaryPage
    BibliographyPage
    
    */

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteCreator' class
     *
     * @author Chimomo
     */
    class Report extends Document {
    
        /**
         * Create pages
         */
        @Override
        public void createPages() {
            this.getPages().add(new IntroductionPage());
            this.getPages().add(new ResultsPage());
            this.getPages().add(new ConclusionPage());
            this.getPages().add(new SummaryPage());
            this.getPages().add(new BibliographyPage());
        }
    
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class ResultsPage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteCreator' class
     *
     * @author Chimomo
     */
    class Resume extends Document {
    
        /**
         * Create pages
         */
        @Override
        public void createPages() {
            this.getPages().add(new SkillsPage());
            this.getPages().add(new EducationPage());
            this.getPages().add(new ExperiencePage());
        }
    
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class SkillsPage extends Page {
    }

package chimomo.learning.java.designpattern.factorymethod.realworld;
    
    /**
     * A 'ConcreteProduct' class
     *
     * @author Chimomo
     */
    class SummaryPage extends Page {
    }

[http_www.captainbed.net]: http://www.captainbed.net/troubleshooter