java - 即使在转换和扫描 nextDouble 后也不是数字错误。 (Java)请帮忙？

Question

我运行该程序时遇到问题。循环和计算工作正常。由于某种原因，它只会计算 50 以下的面积。小数字运行良好，但较大的计算会得到 NaN 结果，这是一个问题。有什么帮助吗？

封装区；

导入java.util.;导入java.text。;

公共(public)类AreaPtTwo {

//this creates a scanner object for the user to input through
final static Scanner sc = new Scanner(System.in);


public static void main (String[] args){
    boolean playAgain = true;
    DecimalFormat fmt = new DecimalFormat("#.###");
    while(playAgain){
        //gets the three inputs from the user
        double a = getNum(1);
        double b = getNum(2);        
        double c = getNum(3);

        // calculates 's' = perimeter/2
        double s = (a+b+c)/2.0;

        //this calculates the area of the triangle by getting the square root of (s(s-a)(s-b)(s-c)) --> this is hard to read but there isn't really a better way to put it in comments.
        double area = (double) Math.sqrt(s*(s-a)*(s-b)*(s-c));

        System.out.println("Area: " + fmt.format(area));

        //Closes 
        System.out.println("_______________________________________________________________________________________________________");
        System.out.println("Play again? (y/n)");
        String again = sc.next();
        if(again.charAt(0) == 'y') playAgain = true;
        else if (again.charAt(0) == 'n') playAgain = false;
        else playAgain = false;
    }
}

// this method is to get the input from the user. It is in a method because it is performed three times. this will only accept numbers, no strings or characers allowed
public static double getNum(int n){
    System.out.println("Enter the length of side " + n +":");

    // this will loop until to make sure that the user does not enter characters or words, and will prompt the user until a number is entered
    while (!sc.hasNextDouble()){
        System.out.println("Invalid input\nEnter the length of side " + n +":");
        sc.next(); // this has to be sc.next() because it will throw a hige error if someone enters a word
    }

    // this returns the next double entered as the variable. 
    return sc.nextDouble();
}

}

Answer 1

从数学上讲，如果边不能构成实际的三角形，则 s(s-a)(s-b)(s-c) 应该为负数，并且负数的平方根返回 Nan。看起来，当你得到 NaN 时，问题出在几何上，而不是编程上。对于任何可以形成实际三角形的数字，它都可以正常工作。
如果您不明白我的意思，请尝试画一个边长分别为 1、2 和 5 的三角形。