现有一块画布上(Canvas)它有如下功能：  定义addShape(Shape s)在画布上新增并绘制出其形状;  定义removeShape(Shape s)删除画布上已存在的形状  定义clone(Shape s)克隆一个已存在的形状增加到画布上  定义Shape Max()方法返回画布上面积最大的形状(如果有相等的几个返回第一个)  定义public double getArea()方法求画布上所有形状的面积和  定义printAllShapes()方法打印画布上所有形状信息 每一个形状(Shape)类，都有创建时的日期数据域(createdDate),创建的颜色（color），求面积和绘制图形的方法等等，每一个形状都是能被比较和复制(复制的时候，形状的时间应该是被复制的时间而不是被复制的形状的创建时间)。长方形和圆形是形状类的子类，它们会重写父类求面积和绘制图形的方法。为了程序实现方便，我们这里只定义两种图形。

好的，这是一个比较完整的画布类，需要实现以下几个方法：

public class Canvas {
    private List<Shape> shapes;

    public Canvas() {
        shapes = new ArrayList<>();
    }

    // 在画布上新增并绘制出一个形状
    public void addShape(Shape s) {
        shapes.add(s);
        s.draw();
    }

    // 删除画布上已存在的形状
    public void removeShape(Shape s) {
        shapes.remove(s);
    }

    // 克隆一个已存在的形状增加到画布上
    public void clone(Shape s) {
        Shape clonedShape = s.clone();
        shapes.add(clonedShape);
        clonedShape.draw();
    }

    // 返回画布上面积最大的形状
    public Shape max() {
        if (shapes.isEmpty()) {
            return null;
        }
        Shape maxShape = shapes.get(0);
        double maxArea = maxShape.getArea();
        for (Shape s : shapes) {
            if (s.getArea() > maxArea) {
                maxShape = s;
                maxArea = s.getArea();
            }
        }
        return maxShape;
    }

    // 求画布上所有形状的面积和
    public double getArea() {
        double totalArea = 0;
        for (Shape s : shapes) {
            totalArea += s.getArea();
        }
        return totalArea;
    }

    // 打印画布上所有形状信息
    public void printAllShapes() {
        for (Shape s : shapes) {
            System.out.println(s.toString());
        }
    }
}

其中，Shape、Rectangle和Circle类的实现如下：

public abstract class Shape implements Cloneable {
    private Date createdDate;
    private String color;

    public Shape(String color) {
        this.createdDate = new Date();
        this.color = color;
    }

    public abstract double getArea();

    public abstract void draw();

    @Override
    public Shape clone() {
        try {
            Shape clonedShape = (Shape) super.clone();
            clonedShape.createdDate = new Date();
            return clonedShape;
        } catch (CloneNotSupportedException e) {
            return null;
        }
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public Date getCreatedDate() {
        return createdDate;
    }

    public void setCreatedDate(Date createdDate) {
        this.createdDate = createdDate;
    }

    @Override
    public String toString() {
        return "Shape{" +
                "createdDate=" + createdDate +
                ", color='" + color + '\'' +
                '}';
    }
}

public class Rectangle extends Shape {
    private double width;
    private double height;

    public Rectangle(String color, double width, double height) {
        super(color);
        this.width = width;
        this.height = height;
    }

    @Override
    public double getArea() {
        return width * height;
    }

    @Override
    public void draw() {
        System.out.println("Drawing a rectangle with color " + getColor());
    }

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    @Override
    public String toString() {
        return "Rectangle{" +
                "createdDate=" + getCreatedDate() +
                ", color='" + getColor() + '\'' +
                ", width=" + width +
                ", height=" + height +
                '}';
    }
}

public class Circle extends Shape {
    private double radius;

    public Circle(String color, double radius) {
        super(color);
        this.radius = radius;
    }

    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }

    @Override
    public void draw() {
        System.out.println("Drawing a circle with color " + getColor());
    }

    public double getRadius() {
        return radius;
    }

    public void setRadius(double radius) {
        this.radius = radius;
    }

    @Override
    public String toString() {
        return "Circle{" +
                "createdDate=" + getCreatedDate() +
                ", color='" + getColor() + '\'' +
                ", radius=" + radius +
                '}';
    }
}