LineIntersect.java

// this implementation has an error in the calculation, find the error

class Point {

    public float x, y;

    public Point(float x, float y) {
        this.x = x;
        this.y = y;
    }
}

class Line {

    public Point p1, p2;
    private float a, b, c;

    public Line(Point p1, Point p2) {
        this.p1 = p1;
        this.p2 = p2;
        
        calculateCoEfficients();
    }

    public Point getIntersectionPoint(Line l2) {
        float x = 0;
        float y = 0;

        // TODO calcuate the intersection point of "this" line and line l2,
        // then set the values to x and y
        // we have two equations
        // (a1)x + (b1)y + (c1) = 0 and
        // (a2)x + (b2)y + (c2) = 0
        float a1 = this.a;
        float b1 = this.b;
        float c1 = this.c;

        float a2 = l2.a;
        float b2 = l2.b;
        float c2 = l2.c;

        // now we need to find the value of x and y
        x = (c2 * b1 - c1 * b2) / (a1 * b2 - a2 * b1);
        y = (a1 * c2 - a2 * c1) / (a2 * b1 - a1 * b2);


        // END OF TODO SECTION
        Point intersectionPoint = new Point(x, y);
        return intersectionPoint;
    }

    public void calculateCoEfficients() {
        // as we know, the euation is (x - x1)/(x1 - x2) = (y - y1)(y1 - y2)
        float x1 = this.p1.x;
        float x2 = this.p2.x;
        float y1 = this.p1.x;
        float y2 = this.p2.y;

        // this we got by solving the eqn (x - x1)/(x1 - x2) = (y - y1)(y1 - y2)
        a = (y1 - y2);
        b = -(x1 - x2);
        c = -x1 * (y1 - y2) + y1 * (x1 - x2);
    }
}

public class LineIntersect {

    public static void main(String[] args) {
        Line l1 = new Line(new Point(-1, -1), new Point(5, 5));
        Line l2 = new Line(new Point(2, -2), new Point(-3, 3));

        Point intersectionPoint = l1.getIntersectionPoint(l2);
        System.out.println("The lines intersect at " + intersectionPoint.x + " in x co-ordinate and " + intersectionPoint.y + " in y co-ordinate");
    }
}