// 5-22 如何運用抽象類。package Demo;abstract class Shape{    int position_x,position_y; // 坐標 變量    void MoveTo(int new_pos_x,int new_pos_y){        position_x=new_pos_x;        position_y=new_pos_y;    }    abstract void draw(); // 抽象方法}class Square extends Shape{    int length;    void draw(){        System.out.println("this is a square.");    }}class  Circle extends Shape{    int radius;    void draw(){        System.out.println("this is a circle.");    }}class Trigon extends Shape{    int bottom;    int highness;    void draw(){        System.out.println("this is a trigon.");    }}class ShapeManager{    void manager(Shape obj){        obj.draw();    }}public class Demo {    public static void main(String args[]){        ShapeManager shape_man=new ShapeManager();        Square sq=new Square();        Circle ci=new Circle();        Trigon tr=new Trigon();        shape_man.manager(sq);        shape_man.manager(ci);        shape_man.manager(tr);    }}