Java、三角形面积

（三角形的面积）
       编写程序，提示用户输入三角形的三个点（x1, y1）、（x2, y2）和（x3, y3），然后显示它的面积。计算三角形面积的公式是：

                s = （边1 + 边2 + 边3） / 2  

               面积 = √（s(s - 边1) (s - 边2) (s - 边3)）

package pack2;

import java.util.Scanner;

import javafx.geometry.Point2D;

public class AreaOfTriangle {

	public static void main(String[] args) {
		try(Scanner input = new Scanner(System.in);) {
			System.out.print("Enter three points for a triangle: ");
			double x1 = input.nextDouble();double y1 = input.nextDouble();
			double x2 = input.nextDouble();double y2 = input.nextDouble();
			double x3 = input.nextDouble();double y3 = input.nextDouble();
			
			System.out.printf("The area of the triangle is %.1fn", 
                                   area(x1, y1, x2, y2, x3, y3));
		}
	}
	
	//三角形面积
	public static double area(double x1, double y1, double x2, double y2, 
                                                     double x3, double y3) {
		Point2D point2d1 = new Point2D(x1, y1);	//创建Point2D对象
		Point2D point2d2 = new Point2D(x2, y2);
		Point2D point2d3 = new Point2D(x3, y3);
		
		double side1 = point2d1.distance(point2d2);	//调用Point2D的方法得到边
		double side2 = point2d1.distance(point2d3);
		double side3 = point2d2.distance(point2d3);
		double s = (side1 + side2 + side3) / 2;
		
		return Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
	}
}