using the following code:

"/** * This file shows you how to find the area of intersection of two circles * *

Time Complexity: O(1) * *

NOTE: This file could use some formal testing. */

import static java.lang.Math.*;

import java.awt.geom.*;

public class CircleCircleIntersectionArea {

private static final double EPS = 1e-6;

// Due to double rounding precision the value passed into the acos // function may be outside its domain of [-1, +1] which would return // the value Double.NaN which we do not want. private static double arccosSafe(double x) { if (x >= +1.0) return 0; if (x <= -1.0) return PI; return acos(x); }

public static double circleCircleIntersectionArea(Point2D c1, double r1, Point2D c2, double r2) {

double r = r1, R = r2; Point2D c = c1, C = c2;

if (r1 > r2) { r = r2; R = r1; c = c2; C = c1; }

double dist = c1.distance(c2); Point2D[] intersections = circleCircleIntersection(c1, r1, c2, r2);

// Smaller circle is contained within larger circle if (intersections == null) { return PI * r * r;

// Circles do not intersect } else if (intersections.length == 0) { return 0;

// One intersection point } else if (intersections.length == 1) {

// Check if the smaller circle is inside larger circle if (dist < R) { return PI * r * r; } else { return 0; }

// Circles intersect at two distinct points } else {

// http://stackoverflow.com/questions/4247889/area-of-intersection-between-two-circles double d = dist; Double part1 = r * r * arccosSafe((d * d + r * r - R * R) / (2 * d * r)); Double part2 = R * R * arccosSafe((d * d + R * R - r * r) / (2 * d * R)); Double part3 = 0.5 * sqrt((-d + r + R) * (d + r - R) * (d - r + R) * (d + r + R));

return part1 + part2 - part3; } }

// Finds the intersection points of two circles. If the smaller circle is contained // within the larger one this method returns null. If there is no intersection point // an empty array is returned. If there is a unique intersection point that point alone // is returned, otherwise two distinct points are returned where the intersection is. public static Point2D[] circleCircleIntersection(Point2D c1, double r1, Point2D c2, double r2) {

// r is the smaller radius and R is bigger radius double r, R;

// c is the center of the small circle // C is the center of the big circle Point2D c, C;

// Determine which is the bigger/smaller circle if (r1 < r2) { r = r1; R = r2; c = c1; C = c2; } else { r = r2; R = r1; c = c2; C = c1; }

double dist = c1.distance(c2);

// There are an infinite number of solutions if (dist < EPS && abs(r - R) < EPS) return null;

// No intersection (small circle contained within big circle) if (r + dist < R) return null;

// No intersection (circles are disjoint) if (r + R < dist) return new Point2D[] {};

// Let (cx, cy) be the center of the small circle // Let (Cx, Cy) be the center of the larger circle double cx = c.getX(); double Cx = C.getX(); double cy = c.getY(); double Cy = C.getY();

// Compute the vector from the big circle to the little circle double vx = cx - Cx; double vy = cy - Cy;

// Scale the vector by R and offset the vector so that the head of the vector // is positioned on the circumference of the big circle ready to be rotated double x = (vx / dist) * R + Cx; double y = (vy / dist) * R + Cy; Point2D point = new Point2D.Double(x, y);

// Unique intersection point on circumference of both circles if (abs(r + R - dist) < EPS || abs(R - (r + dist)) < EPS) return new Point2D[] {point};

// Find the angle via cos law double angle = arccosSafe((r * r - dist * dist - R * R) / (-2.0 * dist * R));

// Two unique intersection points Point2D pt1 = rotatePoint(C, point, angle); Point2D pt2 = rotatePoint(C, point, -angle);

return new Point2D[] {pt1, pt2}; }

// Rotate point 'pt' a certain number of radians clockwise // relative to some fixed point 'fp'. Note that the angle // should be specified in radians, not degrees. private static Point2D rotatePoint(Point2D fp, Point2D pt, double angle) {

double fpx = fp.getX(); double fpy = fp.getY(); double ptx = pt.getX(); double pty = pt.getY();

// Compute the vector from the fixed point // to the point of rotation. double x = ptx - fpx; double y = pty - fpy;

// Apply the clockwise rotation matrix to the vector // | cos(theta) sin(theta) ||x| | xcos(theta) + ysin(theta) | // | -sin(theta) cos(theta) ||y| = | -xsin(theta) + ycos(theta) | double xRotated = x * cos(angle) + y * sin(angle); double yRotated = y * cos(angle) - x * sin(angle);

// The rotation matrix rotated the vector about the origin, so we // need to offset it by the point (fpx, fpy) to get the right answer return new Point2D.Double(fpx + xRotated, fpy + yRotated); } }"

I get the following error when i run it:

"$javac CircleCircleIntersectionArea.java $java -Xmx128M -Xms16M CircleCircleIntersectionArea Error: Main method not found in class CircleCircleIntersectionArea, please define the main method as: public static void main(String[] args) or a JavaFX application class must extend javafx.application.Application"

How can I run the code without this error please?

Answer rating: 100% (QA)

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