Code:
/**
** Java Program to Implement Shoelace Algorithm
**/
import java.util.Scanner;
/** Class Shoelace **/
public class Shoelace
{
/** Function to calculate area **/
public double area(int[][] arr)
{
int n = arr.length;
/** copy initial point to last row **/
arr[n - 1][0] = arr[0][0];
arr[n - 1][1] = arr[0][1];
double det = 0.0;
/** add product of x coordinate of ith point with y coordinate of (i + 1)th point **/
for (int i = 0; i < n - 1; i++)
det += (double)(arr[i][0] * arr[i + 1][1]);
/** subtract product of y coordinate of ith point with x coordinate of (i + 1)th point **/
for (int i = 0; i < n - 1; i++)
det -= (double)(arr[i][1] * arr[i + 1][0]);
/** find absolute value and divide by 2 **/
det = Math.abs(det);
det /= 2;
return det;
}
/** Main function **/
public static void main (String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.println("Shoelace Algorithm Test\n");
/** Make an object of Shoelace class **/
Shoelace s = new Shoelace();
/** Accept number of points **/
System.out.println("\nEnter number of points");
int n = scan.nextInt();
int[][] arr = new int[n + 1][2];
System.out.println("Enter "+ n +" x, y coordinates");
for (int i = 0; i < n; i++)
{
arr[i][0] = scan.nextInt();
arr[i][1] = scan.nextInt();
}
double area = s.area(arr);
System.out.println("\nArea = "+ area);
}
}
Output:
Shoelace Algorithm Test
Enter number of points
5
Enter 5 x, y coordinates
3 4
5 11
12 8
9 5
5 6
Area = 30.0
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