重学设计模式(一) -- 工厂模式

Java 设计模式结构如下：

工厂模式包括：静态工厂模式，工厂方法模式,抽象工厂模式。

在工厂模式中，我们创建对象时不会对客户端暴露出创建逻辑，而是通过使用一个共同的接口来指向新创建的对象。

1. 静态工厂模式

静态工厂模式，也叫做简单工厂模式，是工厂模式中最简单的一个模式。由一个工厂类对象决定创建出哪种产品类的实例。

实现：创建一个 Shape 接口和实现 Shape 接口的实体类，再创建一个工厂类 ShapeFactory,通过工厂类中方法创建出不同类型的对象。

（1）创建 Shape 接口

public interface Shape {
    void draw();
}

（2）创建实现类

public class CircleShape implements Shape {
    @Override
    public void draw() {
    System.out.println("Circle draw()");
    }
}

public class SquareShape implements Shape {
    @Override
    public void draw() {
        System.out.println("SquareShape draw()");
    }
}

public class RectangleShape implements Shape {
    @Override
    public void draw() {
        System.out.println("Rectangle draw()");
    }
}

(3) 创建工厂类

public class ShapeFactory {

    public static Shape createShape(int type) {
        Shape shape = null;
        if (type == 1) {
            shape = new CircleShape();
        } else if (type == 2) {
            shape = new RectangleShape();
        }
        return shape;
    }
}

(4) 客户端调用

public class MainApp {

    public static void main(String[] argbs) {
        Shape shape = ShapeFactory.createShape(1);
        shape.draw();
        shape = ShapeFactory.createShape(2);
        shape.draw();
    }
}

工厂类也可以通过反射进行获取实体对象，避免了通过参数 type 进行判断处理。

public class ShapeFactory {

    public static Shape createShape(Class<? extends Shape> clazz) {
        try {
            Shape shape = clazz.newInstance();
            return shape;
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return null;
    }
}

public class MainApp {

    public static void main(String[] argbs) {
        Shape shape = ShapeFactory.createShape(CircleShape.class);
        shape.draw();

        shape = ShapeFactory.createShape(RectangleShape.class);
        shape.draw();
    }
}

2. 工厂方法模式

当需要增加其他的 Shape类型时，需要增加相应的工厂类，使得代码类成倍增加。

(1) Shape 接口

public interface Shape {

    void draw();
}

(2) Shape 接口实现类

public class CircleShape implements Shape {
    @Override
    public void draw() {
        System.out.println("Circle draw()");
    }
}

public class SquareShape implements Shape {
    @Override
    public void draw() {
        System.out.println("SquareShape draw()");
    }
}

public class RectangleShape implements Shape {
    @Override
    public void draw() {
        System.out.println("Rectangle draw()");
    }
}

(3) 工厂接口类

public interface ShapeMethodFactory {
    Shape createShape();
}

(4) 工厂接口实现类

public class CircleShapeFactory implements ShapeMethodFactory {
    @Override
    public Shape createShape() {
        return new CircleShape();
    }

}

public class RectangleShapeFactory implements ShapeMethodFactory {

    @Override
    public Shape createShape() {
        return new RectangleShape();
    }
}

public class SquareShapeFactory implements ShapeMethodFactory {
    @Override
    public Shape createShape() {
        return new SquareShape();
    }
}

(5) 客户类

public class MainApp {
    public static void main(String[] argbs) {
        ShapeMethodFactory factory = new CircleShapeFactory();
        Shape shape = factory.createShape();
        shape.draw();

        factory = new SquareShapeFactory();
        shape = factory.createShape();
        shape.draw();
    }
}