Charge.java

/* *****************************************************************************
 *  Name:              Ada Lovelace
 *  Coursera User ID:  123456
 *  Last modified:     October 16, 1842
 **************************************************************************** */

public class Charge {
    private final double rx, ry, q;

    public Charge(double x0, double y0, double q0) {
        rx = x0;
        ry = y0;
        q = q0;
    }

    public double potentialAt(double x, double y) {
        double dx = rx - x;
        double dy = ry - y;
        double r = Math.sqrt(dx * dx + dy * dy);
        double k = 8.99e09;
        return k * q / r;
    }

    public String toString() {
        return q + " at " + "(" + rx + ", " + ry + ")";
    }

    public static void main(String[] args) {
        Charge c = new Charge(0.5, 0.5, 20.5);
        System.out.println(c);
        System.out.printf("%.2e\n", c.potentialAt(0.1, 0.98));
    }
}