定义一个图形（shape）类的。子类三角形。。矩形。。继承它的属性；是用java的

abstract class Shape{
int position_x,position_y;//定义坐标
void MoveTo(int new_pos_x,int new_pos_y){
position_x=new_pos_x;
position_y=new_pos_y;
}
abstract void draw();//定义绘制方法
}
class Square extends Shape{
int length;
void draw(){
System.out.println("This is a squre.");
}
}
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(s