public static void main(String[] args) {

Shape shape;

Scanner input = new Scanner(System.in);

System.out.println("请选择图形(1、圆形 2、矩形 3、三角形)");

int a = input.nextInt();

if(a == 1){

System.out.println("请输入圆形的边长：");

double r = input.nextDouble();

shape = new Round(r);

shape.area();

}else if(a == 2){

System.out.println("请输入矩形的底：");

double bottom = input.nextDouble();

System.out.println("请输入矩形的高：");

double high = input.nextDouble();

shape = new Rectangle(bottom, high);

shape.area();

}else if(a == 3){

System.out.println("请输入三角形的底：");

double bottom = input.nextDouble();

System.out.println("请输入三角形的高：");

double high = input.nextDouble();

shape = new Triangle(bottom, high);

shape.area();

}

input.close();

}