Java Program to Implement Shoelace Algorithm

This is a Java Program to Implement Shoelace Algorithm. The shoelace formula, or shoelace algorithm, is a mathematical algorithm to determine the area of a simple polygon whose vertices are described by ordered pairs in the plane

Here is the source code of the Java Program to Implement Shoelace Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

/**
 ** 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