Relationship of X and Y values for P1 and P2:

x values:
x1 < x2
x1 > x2
x1 == x2

y values:
y1 < y2
y1 > y2
y1 == y2

All combinations thereof



Placement of pt1 and pt2:

pt1 in quadrant: 1, 2, 3, 4
pt2 in quadrant 1, 2, 3, 4
All combinations thereof










Line Length:

length == 0
length == 1
length == 2000000000











Line Slope:

[1, 89]
[-89, -1]
horizontal (0)
vertical (90)
nearly horizontal (+ and - slope)
nearly vertical (+ and - slope)












X and Y Coordinate Values:

equivalence classes:
< -1000000000
[-1000000000, -1]
0
[1, 1000000000]
> 1000000000

boundary values:
0
+/- 1000000000
+/- Double.MAX