java基础-多态性

1. 测试案例: Circle.java

abstract class Shape{
    public abstract void draw();
    Shape(){
        System.out.println("start draw()");
        draw();
        System.out.println("finish draw()");
    }
}
public class Circle extends Shape{
    public int radius = 1;
    public void draw(){
        System.out.println(radius);
    }
    Circle(int radius){
        this.radius = radius;
    }
    public static void main(String[] args){
        new Circle(5);
    }
}