Check if point is on line in Java Swing

Question

I have drawn a line and then a point, and then I want to check if the point is on the line or not. I have taken a line coordinate in array (as there was more than one line). I want to check the current point in on the last line or not?

if (positionX1 == positionX2 && positionY1 == positionY2) {
    float m = line.getSlope(
        drawLines[currentLines - 1][2], drawLines[currentLines - 1][3],
        drawLines[currentLines - 1][0], drawLines[currentLines - 1][1]);
    m = Float.parseFloat(df.format(m));
    float c = line.getIntercept(
        drawLines[currentLines - 1][2], drawLines[currentLines - 1][3],
        drawLines[currentLines - 1][0], drawLines[currentLines - 1][1]);
    c = Math.round(c);
    m1 = line.getSlope(positionX2, positionY2,
        drawLines[currentLines - 1][0], drawLines[currentLines - 1][1]);
    m1 = Float.parseFloat(df.format(m1));
    System.out.println(m + "   " + m1);
    c1 = line.getIntercept(positionX2, positionY2,
        drawLines[currentLines - 1][0], drawLines[currentLines - 1][1]);
    c1 = Math.round(c1);

    if (m == m1 && ((c == c1) || (c == c1 - 1) || (c == c1 + 1))) {
        System.out.println("Point is on Line");
    }
}

Problem is when a point is near the starting point of line or when a line is about vertical values of m1 and c1 changes with big difference. So, there's a problem for detecting if a point on line or not. How can I check for this situation?

Answer 1

Line2D.ptSegDist(x1, y1, x2, y2, xP, yP) returns 0.0 if the point (xP, yP) is on the line segment from (x1, y1) to (x2, y2). Line2D.ptLineDist does the same thing for the infinite line.