工厂设计模式

介绍

• 用工厂类的方法代替new，自主实例化对象
• 实现创建和调用的分离

简单工厂

public interface Moveable {    public void run();}

public class Car implements Moveable {    @Override    public void run() {        System.out.println("car is running");           }}

public class Train implements Moveable {        @Override    public void run() {        System.out.println("train is running");    }}

public class MoveableFactory {    public static Moveable createMoveable(String moveable){        if(moveable=="car"){            return new Car();        }else if(moveable=="train"){            return new Train();        }        return null;    }}

public class MyLearn {    public static void main(String[] args) throws Exception {               Moveable moveable = MoveableFactory.createMoveable("train");        moveable.run();  //train is running    }}

• 开闭原则（OCP）：对扩展开放，对修改关闭，即通过创建新的类来扩展，不应在原有代码上改动
• 简单工厂不满足开闭原则，如果增加新的Moveable，需要修改MoveableFactory类的代码，解决方法：工厂方法设计模式

工厂方法

public interface MoveableFactory {    public  Moveable createMoveable();}

public class CarFactory implements MoveableFactory {    @Override    public  Moveable createMoveable() {        return new Car();    }}

public class TrainFactory implements MoveableFactory {    @Override    public Moveable createMoveable() {        return new Train();    }}

    public static void main(String[] args) throws Exception {               Moveable moveable = new CarFactory().createMoveable();        moveable.run();  //car is running    }

• 每次增加一个产品都需要增加一个工厂，造成工厂泛滥
• 可以用反射解决这个问题

public class MoveableFactory {    public static Moveable createMoveable(Class<? extends Moveable> clazz) {        Object object=null;        try {            object = Class.forName(clazz.getName()).newInstance();        } catch (InstantiationException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        } catch (ClassNotFoundException e) {            e.printStackTrace();        }        return (Moveable) object;    }}

public static void main(String[] args) throws Exception {               Moveable moveable = MoveableFactory.createMoveable(Train.class);        moveable.run();      }

抽象工厂

• 创建一套产品族，例如QQ 换肤，一换一整套

public interface AbstractFactory {public Shape createShape();public Color createColor();}

public class AppearanceOne implements AbstractFactory {    @Override    public Shape createShape() {        return new circle();    }    @Override    public Color createColor() {        return new Red();    }}

 public static void main(String[] args) throws Exception {        AbstractFactory f=new AppearanceOne();        Color color = f.createColor();        color.getColor();        Shape shape = f.createShape();        shape.getShape();    }