After reviewing your code, it seems that it's only comparing the slope value and not including calculation for the x or y intercepts. However, shouldn't you include that in your comparisons since two different lines can have the same slope but different x or y intercepts.
I enjoyed reading your code for MaxPointsOnALine.java URL: https://github.com/mengli/leetcode/blob/master/MaxPointsOnALine.java#L30
After reviewing your code, it seems that it's only comparing the slope value and not including calculation for the x or y intercepts. However, shouldn't you include that in your comparisons since two different lines can have the same slope but different x or y intercepts.