5.19(The MyTriangle class)

问题及代码：package first;import java.util.Scanner;public class MyTriangle {public static void main(String[] args) {System.out.println("请输入一个三角形的三边：");Scanner a=new Scanner(System.in);double s=0;while(true){double side1=a.nextDouble();double side2=a.nextDouble();double side3=a.nextDouble();if(isValid(side1, side2, side3)){s=area(side1, side2,  side3);break;}else{System.out.println("输入非法，请重新输入！");}}System.out.println("该三角形的面积为："+s);}public static boolean isValid(double side1, double side2, double side3) {boolean a = false;if ((side1 + side2 > side3) && (side2 + side3 > side1)&& (side3 + side1 > side2))a = true;return a;}public static double area(double side1, double side2, double side3) {double s = 0;if (isValid(side1, side2, side3)) {double b = (side1 + side2 + side3) / 2;s = Math.sqrt(b * (b - side1) * (b - side2) * (b - side3));}return s;}}运行结果：