Using a more efficient algorithm to calculate the area of ​​a polygon in Java

The word "polygon" comes from the Greek "Poly" meaning "many" and "gon" meaning "angle". A polygon is a two-dimensional closed plane shape connected by three or more straight lines. For example triangle, quadrilateral, hexagon, etc.

Although there are many ways to find the area of ​​a polygon in this article, we will use the slicker algorithm for this purpose.

A more flexible algorithm for finding the area of ​​a polygon

Slicker Algorithm

There are two facts you must know. First, according to mathematical convention, points in the y direction upward are always positive. Secondly, according to the computer system, the y-direction points downward and is always positive. This algorithm provides an efficient solution by listing the vertices counterclockwise using positive y-down coordinates. It will cancel out both of these facts, creating a positive zone.

Now let's discuss a java program that implements the slicker algorithm.

algorithm

• Step 1 - Create a class "Slicker" and its two inner classes "Coordinates" and "Poly".

• Step 2 - Declare and initialize the constant "MAXIMUM" to limit the number of sides of the polygon.

• Step 3 - Create an array of objects of class "Coordinates" inside the inner class "Poly". Then, create a constructor of the "Poly" class to store the coordinates in that object array.

• Step 4 - Further define the method "calcAr" and the parameter "cr". In this method, we will create a for loop that will run to the number of sides of the polygon and calculate the area.

• Step 5 - Now in the main method, create an object "cr" of class "Poly". We will then get the number of sides and coordinates of the polygon from the user.

• Step 6 - Finally, we will call the method "calcAr" and check if the area is positive or negative using an if-else block. If positive, the "if" block statement is executed, otherwise the else block is executed.

Example

import java.util.*;
public class Slicker {
   // to signify maximum number of sides of polygon
   static final int MAXIMUM = 50; 
   static class Coordinates {
      double c1, c2; 
      // declaring coordinates
   }
   static class Poly {
      // Array object of class Coordinates
      Coordinates cr[] = new Coordinates[MAXIMUM];
      int sides;
      Poly() 
      // constructor
      {
         // to accept input of coordinates
         for (int i = 0; i < MAXIMUM; i++)
         cr[i] = new Coordinates();
      }
   }
   // method to calculate area
   static double caclAr(Poly cr) {
      double res = 0;
      for (int i = 0; i < cr.sides; i++) {
         int j = (i + 1) % cr.sides;
         res += (cr.cr[i].c1 * cr.cr[j].c2)
          - (cr.cr[j].c1 * cr.cr[i].c2);
      }
      return res / 2;
   }
   static public void main(String[] args)
   {
      Poly cr = new Poly(); 
      // object of class 'Poly'
      // Object of scanner class for User inputs
      Scanner in = new Scanner(System.in);
      System.out.print("Enter total number of sides: ");
      cr.sides = in.nextInt();
      // to take coordinates from user
      System.out.println("Enter c1 and c2 coordinates: ");
      for (int i = 0; i < cr.sides; i++) {
         cr.cr[i].c1 = in.nextDouble();
         cr.cr[i].c2 = in.nextDouble();
      }
      // calling user defined method
      double caclAr = caclAr(cr);
      if (caclAr > 0) {
         System.out.print("The area of given Polygon: " + caclAr);
      } else {
         System.out.print("The area of given Polygon: " + (caclAr * -1));
      }
   }
} 

Output

Enter total number of sides: 4
Enter c1 and c2 coordinates: 
2 3
3 5
5 8
8 2
The area of given Polygon: 17.0

in conclusion

No planar shape can be considered a polygon, such as a circle, although it is a closed planar shape without any sides. So we can't call it a polygon. In this article, we have created a java program to calculate the area of ​​a polygon using slicker algorithm.

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