使用java實(shí)現(xiàn)的訪問者模式的示例，對訪問者模式的對象結(jié)構(gòu)和操作分離的思想摸不透徹，敲下代碼，加深印象

public class VisitorMode {

    public static void main(String[] args) {
        AeraShapeVisitor aeraShapeVisitor = new AeraShapeVisitor();
        Shape circle = new Circle(10);
        circle.accept(aeraShapeVisitor);
        System.out.println("area = "+aeraShapeVisitor.getmArea());

        PerimeterShapeVisitor perimeterShapeVisitor = new PerimeterShapeVisitor();
        circle.accept(perimeterShapeVisitor);
        System.out.println("perimeter = "+perimeterShapeVisitor.getmPerimeter());

        Rectangle rectangle =new Rectangle(10,10);
        rectangle.accept(aeraShapeVisitor);
        System.out.println("area = "+aeraShapeVisitor.getmArea());

        rectangle.accept(perimeterShapeVisitor);
        System.out.println("perimeter = "+perimeterShapeVisitor.getmPerimeter());
    }

    private static interface ShapeVisitor{
        void visitor(Circle circle);
        void visitor(Rectangle circle);
    }

    private static class AeraShapeVisitor implements ShapeVisitor{
        private double mArea;
        @Override
        public void visitor(Circle circle) {
            mArea =  Math.PI * circle.mRadius * circle.mRadius;
        }

        @Override
        public void visitor(Rectangle rectangle) {
            mArea = rectangle.mHeight * rectangle.mHeight;
        }

        public double getmArea() {
            return mArea;
        }
    }

    private static class PerimeterShapeVisitor implements ShapeVisitor{
        private double mPerimeter;
        @Override
        public void visitor(Circle circle) {
            mPerimeter =  2 * Math.PI * circle.mRadius;
        }

        @Override
        public void visitor(Rectangle rectangle) {
            mPerimeter = 2 * (rectangle.mHeight + rectangle.mHeight);
        }

        public double getmPerimeter() {
            return mPerimeter;
        }
    }

    private static  interface Shape{
        void accept(ShapeVisitor visitor);
    }
    private static class Circle implements Shape{
        private int mRadius;

        public Circle(int mRadius) {
            this.mRadius = mRadius;
        }

        @Override
        public void accept(ShapeVisitor visitor) {
            visitor.visitor(this);
        }
    }

    private static class Rectangle implements Shape{
        private int mWidth;
        private int mHeight;

        public Rectangle(int mWidth, int mHeight) {
            this.mWidth = mWidth;
            this.mHeight = mHeight;
        }

        @Override
        public void accept(ShapeVisitor visitor) {
            visitor.visitor(this);
        }
    }
}