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Monday, 29 August 2016

Chapter 8 Exercise 32, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

8.32 (Geometry: area of a triangle) Write a method that returns the area of a triangle
using the following header:
public static double getTriangleArea(double[][] points)
The points are stored in a 3-by-2 two-dimensional array points with points[0]
[0] and points[0][1] for ( x1 , y1 ). The triangle area can be computed using the
formula in Programming Exercise 2.19. The method returns 0 if the three points
are on the same line. Write a program that prompts the user to enter three points of
a triangle and displays the triangle's area. Here is a sample run of the program:
Enter x1, y1, x2, y2, x3, y3: 2.5 2 5 -1.0 4.0 2.0
The area of the triangle is 2.25
Enter x1, y1, x2, y2, x3, y3: 2 2 4.5 4.5 6 6
The three points are on the same line


import java.util.Scanner;

public class Exercise_32 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        double[][] points = new double[3][2];
        System.out.print("Enter x1 y1 x2 y2 x3 y3: ");
        for (int i = 0; i < points.length; i++)
            for (int j = 0; j < points[i].length; j++)
                points[i][j] = input.nextDouble();

        double area = getTriangleArea(points);

        if (area == 0) {
            System.out.println("The three points are on the same line");
        }
        else {
            System.out.println("The area of the triangle is " + area);
        }
    }

    public static double getTriangleArea(double[][] points) {


        double side1 = distanceBetweenTwoPoints(points[0][0], points[0][1], points[1][0], points[1][1]);
        double side2 = distanceBetweenTwoPoints(points[0][0], points[0][1], points[2][0], points[2][1]);
        double side3 = distanceBetweenTwoPoints(points[2][0], points[2][1], points[1][0], points[1][1]);
        double s = (side1 + side2 + side3) / 2;
        double area = s * (s - side1) * (s - side2) * (s - side3);

        if (area < 0.000001)
            return 0;
        else
            return Math.sqrt(area);
    }

    public static double distanceBetweenTwoPoints(double x1, double y1, double x2, double y2) {
        return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    }

}

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