package Shape;

abstract public class Shape {
    abstract double getArea();
}
class Circle extends Shape{
    private double r;
    public Circle(double r){
        this.r=r;
    }
    @Override
    double getArea(){
        return Math.PI*r*r;
    }
}

class Rectangle extends Shape{
    private double chang;
    private double kuan;
    public Rectangle(double chang,double kuan){
        this.chang=chang;
        this.kuan=kuan;
    }
    @Override
    double getArea(){
        return chang*kuan;
    }
}

class Triangle extends Shape{
    private double di;
    private double height;
    public Triangle(double di,double height){
        this.di=di;
        this.height=height;
    }
    @Override
    double getArea(){
        return 0.5*di*height;
    }
}

class ShapeUtil{
    public static void printArea(Shape shape){
        System.out.println("面积是"+shape.getArea());
    }
}