Help me my assignment!!!

Question

Now you have to think. In many areas of science (e.g., computer graphics, computational geometry, image analysis, robotics, physics) , it is often necessary to determine whether or not two line segments intersect. Assume that we have two 2D line segments one line segment has endpoints (Ax,Ay) and (Bx,By) and the other segment has endpoints (Cx,Cy) and (Dx,Dy).
Write a static main method for a class called IntersectionTester that asks the user for the eight values of the integer coordinates for two line segments and then displays a message indicating whether or not the line segments intersect. Assume that all coordinates are entered as integer values. Here are two equations which you must use to determine whether or not the intersection occurs:
(1 - s)Ax + sBx = (1-t)Cx + tDx
(1 - s)Ay + sBy = (1-t)Cy + tDy
You will need to solve for s and t and see if both s and t lie in the decimal range from 0 to 1. Your output should display the entered values and the result in a format similar to this:
Enter coordinates:
Ax = 2
Ay = 8
Bx = 5
By = 5
Cx = 5
Cy = 7
Dx = 1
Dy = 3
Line segment (2,8)(5,5) intersects with segment (5,7)(1,3).
Make sure to test at least each of the following cases:
i) parallel horizontal lines that intersect
ii) parallel horizontal lines that do not intersect
iii) parallel vertical lines that intersect
iv) parallel vertical lines that do not intersect
v) non-parallel lines that intersect
vi) non-parallel lines that do not intersect
You should also hand in a single picture (.gif or .jpg file using a Paint program) showing properly scaled drawings of ALL of your test cases so that the TA knows what you tested. Each linesegment should have its endpoints properly labelled with the values you entered during testing. Note that to do this part, you'll need to understand the "if" statement which is described in notes #4. Here is an idea as to how you will use it (replace the green code with your own java statements):
if (/*there is an intersection */) {
//DO SOMETHING
else {
//DO SOMETHING ELSE
following is my code:
public class Intersection {
     public void isitintersect() {
          int Ax,Ay,Bx,By,Cx,Cy,Dx,Dy;
          System.out.println("Enter segment endpoints :");
          Ax = Keyboard.getInteger();
          Ay = Keyboard.getInteger();
          Bx = Keyboard.getInteger();
          By = Keyboard.getInteger();
          Cx = Keyboard.getInteger();
          Cy = Keyboard.getInteger();
          Dx = Keyboard.getInteger();
          Dy = Keyboard.getInteger();
     double s = ((Ax-Cx) + (((Cy-Ay)+s * (Ay-By))/(Cy-Dy))*(Cx-Dx));
     double t = (((Cy-Ay) + (((Ax-Cx) + t * (Cx-Dx))/(Ax-Bx)) * (Ay-By))/(Cy-Dy));
     if ((s>0)&&(s<1)&&(t>0)&&(t<1))
System.out.println("Line segment"+(AxAyBxBy)+"intersects with segment"+(CxCyDxDy));
else
System.out.println("Sorry,It can not intersect for ever.");
QUESTION:
I input any integer, the computer tell me it is not intersect.

Answer 1

I'd rewrite this as a matrix equation, where s and t are the unknowns to solve for. (The inverse of the matrix is easy to calculate by hand.)
Degenerate cases are flagged by a zero determinant in this case - no inverse is possible.
It'd be an elegant solution to the problem. Try it and see.