设计模式之工厂模式

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本文介绍了三种常见的设计模式——简单工厂模式、工厂方法模式和抽象工厂模式，通过实例展示了如何创建对象及其在软件开发中的应用场景。从创建对象的灵活性、延迟决策到产品族的统一管理，这些模式有助于提高代码的可维护性和扩展性。

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一、简单工厂模式

简单工厂模式是由一个工厂对象决定创建哪一种产品类的实例。在软件开发中，当我们会用到大量的创建某种、某类或某批对象时，就会使用到工厂模式。

//简单工厂类
public class SimpleFactory {
	//简单工厂模式 也叫 静态工厂模式

	public static Pizza createPizza2(String orderType) {

		Pizza pizza = null;

		System.out.println("使用简单工厂模式2");
		if (orderType.equals("greek")) {
			pizza = new GreekPizza();
			pizza.setName(" 希腊披萨 ");
		} else if (orderType.equals("cheese")) {
			pizza = new CheesePizza();
			pizza.setName(" 奶酪披萨 ");
		} else if (orderType.equals("pepper")) {
			pizza = new PepperPizza();
			pizza.setName("胡椒披萨");
		}

		return pizza;
	}

}

二、工厂方法模式

定义一个创建对象的抽象方法，由于子类决定要实例化的类，工厂方法模式将对象的创建推迟到子类。

package designPatterns.builder.factoryMethod;

/**
 * 工厂方法是一种创建型设计模式， 解决了在不指定具体类的情况下创建产品对象的问题。
 * 其在父类中提供一个创建对象的方法， 允许子类决定实例化对象的类型。
 * @author TEENWAY
 * @since 2020-08-23 16:23:48
 */

/**
 * 通用产品接口
 */
public interface Button {
    void render();
    void onClick();
}

package designPatterns.builder.factoryMethod;

/**
 * Base factory class. Note that "factory" is merely a role for the class. It
 * should have some core business logic which needs different products to be
 * created.
 */
public abstract class Dialog {

    public void renderWindow() {
        // ... other code ...

        Button okButton = createButton();
        okButton.render();
    }

    /**
     * Subclasses will override this method in order to create specific button
     * objects.
     */
    public abstract Button createButton();
}

package designPatterns.builder.factoryMethod;


/**
 * HTML button implementation.
 */
public class HtmlButton implements Button {

    public void render() {
        System.out.println("<button>Test Button</button>");
        onClick();
    }

    public void onClick() {
        System.out.println("Click! Button says - 'Hello World!'");
    }
}

package designPatterns.builder.factoryMethod;


/**
 * HTML Dialog will produce HTML buttons.
 */
public class HtmlDialog extends Dialog {

    @Override
    public Button createButton() {
        return new HtmlButton();
    }
}

package designPatterns.builder.factoryMethod;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

/**
 * Windows button implementation.
 */
public class WindowsButton implements Button {
    JPanel panel = new JPanel();
    JFrame frame = new JFrame();
    JButton button;

    public void render() {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel label = new JLabel("Hello World!");
        label.setOpaque(true);
        label.setBackground(new Color(235, 233, 126));
        label.setFont(new Font("Dialog", Font.BOLD, 44));
        label.setHorizontalAlignment(SwingConstants.CENTER);
        panel.setLayout(new FlowLayout(FlowLayout.CENTER));
        frame.getContentPane().add(panel);
        panel.add(label);
        onClick();
        panel.add(button);

        frame.setSize(320, 200);
        frame.setVisible(true);
        onClick();
    }

    public void onClick() {
        button = new JButton("Exit");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                frame.setVisible(false);
                System.exit(0);
            }
        });
    }
}

package designPatterns.builder.factoryMethod;

/**
 * Windows Dialog will produce Windows buttons.
 */
public class WindowsDialog extends Dialog {

    @Override
    public Button createButton() {
        return new WindowsButton();
    }
}

package designPatterns.builder.factoryMethod;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {
    private static Dialog dialog;

    public static void main(String[] args) {
        configure();
        runBusinessLogic();
    }

    /**
     * The concrete factory is usually chosen depending on configuration or
     * environment options.
     */
    private static void configure() {
        if (System.getProperty("os.name").equals("Windows 7")) {
            dialog = new WindowsDialog();
        } else {
            dialog = new HtmlDialog();
        }
    }

    /**
     * All of the client code should work with factories and products through
     * abstract interfaces. This way it does not care which factory it works
     * with and what kind of product it returns.
     */
    private static void runBusinessLogic() {
        dialog.renderWindow();
    }
}

Test Button
Click! Button says - ‘Hello World!’

Process finished with exit code 0

三、抽象工厂模式

定义一个接口，用于创建相关或有依赖关系的对象簇，而无需指明具体类。

package designPatterns.builder.abstractFactory;

/**
 * Abstract Factory assumes that you have several families of products,
 * structured into separate class hierarchies (Button/Checkbox). All products of
 * the same family have the common interface.
 *
 * This is the common interface for buttons family.
 */
public interface Button {
    void paint();
}

package designPatterns.builder.abstractFactory;

/**
 * Checkboxes is the second product family. It has the same variants as buttons.
 */
public interface Checkbox {
    void paint();
}

package designPatterns.builder.abstractFactory;

/**
 * 抽象工厂是一种创建型设计模式， 它能创建一系列相关的对象， 而无需指定其具体类。
 *
 * 抽象工厂定义了用于创建不同产品的接口， 但将实际的创建工作留给了具体工厂类。 每个工厂类型都对应一个特定的产品变体。
 *
 * 在创建产品时， 客户端代码调用的是工厂对象的构建方法， 而不是直接调用构造函数 （ new 操作符）。 由于一个工厂对应一种产品变体， 因此它创建的所有产品都可相互兼容。
 *
 * 客户端代码仅通过其抽象接口与工厂和产品进行交互。 该接口允许同一客户端代码与不同产品进行交互。 你只需创建一个具体工厂类并将其传递给客户端代码即可。
 * Abstract factory knows about all (abstract) product types.
 */
public interface GUIFactory {
    Button createButton();
    Checkbox createCheckbox();
}

package designPatterns.builder.abstractFactory;

/**
 * All products families have the same varieties (MacOS/Windows).
 *
 * This is a MacOS variant of a button.
 */
public class MacOSButton implements Button {

    @Override
    public void paint() {
        System.out.println("You have created MacOSButton.");
    }
}

package designPatterns.builder.abstractFactory;

/**
 * All products families have the same varieties (MacOS/Windows).
 *
 * This is a variant of a checkbox.
 */
public class MacOSCheckbox implements Checkbox {

    @Override
    public void paint() {
        System.out.println("You have created MacOSCheckbox.");
    }
}

package designPatterns.builder.abstractFactory;

/**
 * Each concrete factory extends basic factory and responsible for creating
 * products of a single variety.
 */
public class MacOSFactory implements GUIFactory {

    @Override
    public Button createButton() {
        return new MacOSButton();
    }

    @Override
    public Checkbox createCheckbox() {
        return new MacOSCheckbox();
    }
}

package designPatterns.builder.abstractFactory;

/**
 * All products families have the same varieties (MacOS/Windows).
 *
 * This is another variant of a button.
 */
public class WindowsButton implements Button {

    @Override
    public void paint() {
        System.out.println("You have created WindowsButton.");
    }
}

package designPatterns.builder.abstractFactory;

/**
 * All products families have the same varieties (MacOS/Windows).
 *
 * This is another variant of a checkbox.
 */
public class WindowsCheckbox implements Checkbox {

    @Override
    public void paint() {
        System.out.println("You have created WindowsCheckbox.");
    }
}

package designPatterns.builder.abstractFactory;

/**
 * Each concrete factory extends basic factory and responsible for creating
 * products of a single variety.
 */
public class WindowsFactory implements GUIFactory {

    @Override
    public Button createButton() {
        return new WindowsButton();
    }

    @Override
    public Checkbox createCheckbox() {
        return new WindowsCheckbox();
    }
}

package designPatterns.builder.abstractFactory;

/**
 * Factory users don't care which concrete factory they use since they work with
 * factories and products through abstract interfaces.
 */
public class Application {
    private Button button;
    private Checkbox checkbox;

    public Application(GUIFactory factory) {
        button = factory.createButton();
        checkbox = factory.createCheckbox();
    }

    public void paint() {
        button.paint();
        checkbox.paint();
    }
}

package designPatterns.builder.abstractFactory;

/**
 * Demo class. Everything comes together here.
 * @since 2020-08-23 17:27:32
 */
public class Demo {

    /**
     * Application picks the factory type and creates it in run time (usually at
     * initialization stage), depending on the configuration or environment
     * variables.
     */
    private static Application configureApplication() {
        Application app;
        GUIFactory factory;
        String osName = System.getProperty("os.name").toLowerCase();
        if (osName.contains("mac")) {
            factory = new MacOSFactory();
            app = new Application(factory);
        } else {
            factory = new WindowsFactory();
            app = new Application(factory);
        }
        return app;
    }

    public static void main(String[] args) {
        Application app = configureApplication();
        app.paint();
    }
}