Untitled

public class Quadrilateral extends Shape {
      XYCoord b, c, d;

    public Quadrilateral(XYCoord a, XYCoord b, XYCoord c, XYCoord d) {
        super(a);
        this.b = b;
        this.c = c;
        this.d = d;
    }

    public double sideLength(XYCoord p1, XYCoord p2) {
        return p1.distance(p2);
    }

    public double perimeter() {
        return sideLength(a, b) + sideLength(b, c) + sideLength(c, d) + sideLength(d, a);
    }

    public double area() {
        double s1 = (sideLength(a, b) + sideLength(b, c) + sideLength(c, a)) / 2;
        double s2 = (sideLength(a, d) + sideLength(d, c) + sideLength(c, a)) / 2;
        return Math.sqrt(s1 * (s1 - sideLength(a, b)) * (s1 - sideLength(b, c)) * (s1 - sideLength(c, a))) +
                Math.sqrt(s2 * (s2 - sideLength(a, d)) * (s2 - sideLength(d, c)) * (s2 - sideLength(c, a)));
    }
}


public class Square extends Quadrilateral {
    private double length;

    public Square(XYCoord anchor, double length) {
        super(anchor, new XYCoord(anchor.getX() + length, anchor.getY()),
                new XYCoord(anchor.getX() + length, anchor.getY() + length),
                new XYCoord(anchor.getX(), anchor.getY() + length));
        this.length = length;
    }

    public void setLength(double newLength) {
        this.length = newLength;
        XYCoord b = new XYCoord(this.a.getX() + newLength, this.a.getY());
        XYCoord c = new XYCoord(this.a.getX() + newLength, this.a.getY() + newLength);
        XYCoord d = new XYCoord(this.a.getX(), this.a.getY() + newLength);
        this.b = b;
        this.c = c;
        this.d = d;
    }

    public double getLength() {
        return this.length;
    }

    public double area() {
        return length * length;
    }

    public double perimeter() {
        return 4 * length;
    }
}

public class Circle extends Shape {
   private double radius;

   public Circle(XYCoord center, double radius) {
      super(center);
      this.radius = radius;
   }

   /** Returns the radius of this circle. */
   public double getRadius() {
      return this.radius;
   }

   /** Changes the radius of this circle. */
   public void setRadius(double newRadius) {
      this.radius = newRadius;
   }

   /** Computes and returns the area of this circle. */
   public double area() {
      return Math.PI * this.radius * this.radius;
   }

   /** Computes and returns the perimeter of this circle. */
   public double perimeter() {
      return 2 * Math.PI * this.radius;
   }

   @Override
   public String toString() {
      return String.format("Circle with center at %s and radius %.3f", this.getAnchor(), this.radius);
   }
}

public class Triangle extends Shape {

    private XYCoord b, c;

    public Triangle(XYCoord a, XYCoord b, XYCoord c) {
        super(a);
        this.b = b;
        this.c = c;
    }

    public XYCoord getB() {
        return b;
    }

    public XYCoord getC() {
        return c;
    }

    public void setBC(XYCoord newB, XYCoord newC) {
        this.b = newB;
        this.c = newC;
    }

    @Override
    public double area() {
        double ab = a.distance(b);
        double ac = a.distance(c);
        double bc = b.distance(c);
        double s = (ab + ac + bc) / 2.0;
        return Math.sqrt(s * (s - ab) * (s - ac) * (s - bc));
    }

    @Override
    public double perimeter() {
        return a.distance(b) + a.distance(c) + b.distance(c);
    }
}