hash value for a line object

Here is a reference implementation of Line object, my confusion is from line 40 to line 43, the question is, if two lines are different, but the OR results of slope/intercept happens to be the same, will it have any issues (e.g. treat different lines the same because of the same hash values)? Since I think same hash value means the same Line.

If the current implementation for hash value do have the issue I mentioned, appreciate if anyone could help to provide some insights what are good implementation for hash value in my case.

1 public static Line findBestLine(GraphPoint[] points) {
2 Line bestLine = null;
3 HashMap<Line, Integer> line_count = new HashMap<Line, Integer>();
4 for (int i = 0; i < points.length; i++) {
5 for (int j = i + 1; j < points.length; j++) {
6 Line line = new Line(points[i], points[j]);
7 if (!line_count.containsKey(line)) {
8 line_count.put(line, 0);
9 }
10 line_count.put(line, line_count.get(line) + 1);
11 if (bestLine == null ||
12 line_count.get(line) > line_count.get(bestLine)) {
13 bestLine = line;
14 }
15 }
16 }
17 return bestLine;
18 }
19
20 public class Line {
21 private static double epsilon = .0001;
22 public double slope;
23 public double intercept;
24 private boolean infinite_slope = false;
25 public Line(GraphPoint p, GraphPoint q) {
26 if (Math.abs(p.x - q.x) > epsilon) { // if x’s are different
27 slope = (p.y - q.y) / (p.x - q.x); // compute slope
28 intercept = p.y - slope * p.x; // y intercept from y=mx+b
29 } else {
30 infinite_slope = true;
31 intercept = p.x; // x-intercept, since slope is infinite
32 }
33 }
34
35 public boolean isEqual(double a, double b) {
36 return (Math.abs(a - b) < epsilon);
37 }
38
39 @Override
40 public int hashCode() {
41 int sl = (int)(slope * 1000);
42 int in = (int)(intercept * 1000);
43 return sl | in;
44 }
45
46 @Override
47 public boolean equals(Object o) {
48 Line l = (Line) o;
49 if (isEqual(l.slope, slope) && isEqual(l.intercept, intercept)
50 && (infinite_slope == l.infinite_slope)) {
51 return true;
52 }
53 return false;
54 }
55 }