写出如下程序的输出结果。 abstract class Shape { public abstract double area(); public void print() { System.out.println(this.area()); } } class Circle extends Shape { private double radius; public Circle(double radius) { this.radius = radius; } public final double area() { return Math.PI*this.radius*this.radius; } } class Rectangle extends Shape { protected double length; protected double width; public Rectangle(double length, double width) { this.length = length; this.width = width; } public double area() { return this.width * this.length; } } public class Test { public static void main(String args[]) { Shape sh = new Circle(10); sh.print(); sh = new Rectangle(4,5); sh.print(); } }