Question

I’m trying to call angles from from the angle method down below in the Rotate90 method but I’m not sure of the syntax. What is the correct syntax?

import java.lang.Math;
public class CartesianPoint implements Point
{
    private double xCoord;
    private double yCoord;

  public CartesianPoint (double xCoordinate,double yCoordinate)
  {
      xCoord = xCoordinate;
      yCoord = yCoordinate;
  }

public double xCoordinate ()
 {
     return xCoord; 
 }

 public double yCoordinate ()
 {
     return yCoord;
 }

 public double angle ()
 {
    double angles;
    angles = Math.cos( xCoord / Math.sqrt( xCoord*xCoord + yCoord*yCoord)); 
    return angles;
 }

 public double radius ()
 {
    double radius;
    radius = (yCoord*yCoord + xCoord*xCoord); //?
    return radius;
 }

public Point rotate90()
{
  double rotated;
  rotated = angles.angle + 90.0; //██████████ Error here ██████████
  return rotated;
}

public double distanceFrom(Point other)
{
  return 0;
}

}

Answer 1

I think you mean

rotated = angle() + 90.0;

Except I think you’ll find that Math.cos uses radians not degrees, so you’re not going to get the result you think you are. And shouldn’t that be arc cos, not cosine? Something like this might be more what you’re looking for:

public double angle()
{
  return Math.atan2(ycoord, xcoord) * 180 / Math.PI;
}

If you want rotate90 to return a new Point that is 90 degrees from the current point, then change it to the following:

   public Point rotate90()
   {
      return new CartesianPoint(-yCoord, xCoord);
   }