Java Program to Apply Above-Below-on Test to Find the Position of a Point with respect to a Line

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This is a Java Program to check whether a point lies below, above or on the line. For any point t (xt, yt) on the plane, its position with respect to the line L connecting p and q is found by calculating the scalar s:
s = A xt + B yt + C
If s < 0, t lies in the clockwise halfplane of L; if s > 0, t lies on the counter-clockwise halfplane; if s = 0, t lies on L.
For example, the equation of the line connecting points (2, 2) and (4, 5) is -3x + 2y + 2 = 0. The point (6, 3) lies in the clockwise halfplane of this line, because (-3)(6) + (2)(3) + 2 = -10. Conversely, the point (0, 5) lies in the other halfplane as (-3)(0) +(2)(5) +2 = 12.

Here is the source code of the Java Program to Apply Above-Below-on Test to Find the Position of a Point with respect to a Line. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

  1. //This is a java program to check whether a point lies on, above or below the gievn line
  2. import java.util.Random;
  3. import java.util.Scanner;
  4.  
  5. public class Position_Point_WRT_Line
  6. {
  7.     public static void main(String args[])
  8.     {
  9.         Random random = new Random();
  10.         int x1, x2, y1, y2;
  11.         x1 = random.nextInt(10);
  12.         x2 = random.nextInt(10);
  13.         y1 = random.nextInt(10);
  14.         y2 = random.nextInt(10);
  15.  
  16.         System.out.println("The Equation of the line is : (" + (y2 - y1)
  17.                 + ")x+(" + (x1 - x2) + ")y+(" + (x2 * y1 - x1 * y2) + ") = 0");
  18.  
  19.         System.out.println("Enter the point : <x>,<y>");
  20.         Scanner scan = new Scanner(System.in);
  21.         int x, y;
  22.         x = scan.nextInt();
  23.         y = scan.nextInt();
  24.  
  25.         int s = (y2 - y1) * x + (x1 - x2) * y + (x2 * y1 - x1 * y2);
  26.         if (s < 0)
  27.             System.out
  28.                     .println("The point lies below the line or left side of the line");
  29.         else if (s > 0)
  30.             System.out
  31.                     .println("The point lies above the line or right side of the line");
  32.         else
  33.             System.out.println("The point lies on the line");
  34.         scan.close();
  35.     }
  36. }

Output:

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$ javac Position_Point_WRT_Line.java
$ java Position_Point_WRT_Line
 
The Equation of the line is : (-2)x+(-9)y+(81) = 0
Enter the point : <x>,<y>
2
3
The point lies above the line or right side of the line

Sanfoundry Global Education & Learning Series – 1000 Java Programs.

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Here’s the list of Best Reference Books in Java Programming, Data Structures and Algorithms.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn