Java OOP 中的 NaN 输出

Question

我刚刚开始学习 Java，我正在尝试使用 OOP 概念创建一个简单的 BMI 计算器。

这是我的代码：

import java.util.Scanner;

class BIM 
{
    int weight;
    double weightKG = weight * 0.45359237;
    int height;
    double heightMETERS = height * 0.0254;
    double BMI = weightKG / (heightMETERS * heightMETERS);
    public void calculateBMI()
    {    
        System.out.print("The BMI is: " + BMI);
    }
}

public class BMI 
{
    public static void main(String args[] ) throws Exception 
    {
        Scanner input = new Scanner(System.in);
        
        System.out.print("Enter weight in pounds: ");
        int weight = input.nextInt();
        
        System.out.print("Enter height in inches: ");
        int height = input.nextInt();
        
        BIM b = new BIM();
        b.calculateBMI(); 
    }
    
    private static void bmiCategory (double BMI)
    {
    
        if (BMI < 18.5)
        {
            System.out.println("Underweight");
        }
        else if (BMI < 25.0)
        {
            System.out.println("Normal");
        }
        else if (BMI < 30.0)
        {
            System.out.println("Overweight");
        }
        else
        {
            System.out.println("Obese");
        }            
    }
}

我的代码的输出：

输入体重（磅）：100 输入高度（英寸）：50 BMI 为：NaN

为什么我得到输出 NaN？另外，为什么不显示类别？

Answer 1

您的

BIM

类会完成所有数学运算，但您从未将

height

或

weight

传递给它（并且在将这些值分配到任何地方之前先进行数学运算）。首先，修复

BIM

。比如，

class BIM {
    public BIM(int weight, int height) {
        this.weight = weight;
        this.height = height;
        this.weightKG = weight * 0.45359237;
        this.heightMETERS = height * 0.0254;
        this.BMI = weightKG / (heightMETERS * heightMETERS);
    }

    int weight;
    double weightKG;
    int height;
    double heightMETERS;
    double BMI;

    public void calculateBMI() {
        System.out.print("The BMI is: " + BMI);
    }
}

然后代替

BIM b = new BIM();

你需要

BIM b = new BIM(weight, height);

Answer 2

错误1
您没有为

BMI 类

的对象设置

weight

和 height 属性的值。您需要在您的BMI类中添加以下代码：

BIM(int weight, int height){
   this.weight = weight;
   this.height = height;
}

然后创建一个BMI类的对象作为

BIM b = new BIM(weight, height);//passing parameters to constructor

错误2
您没有在任何地方调用

bmiCategory

函数，因此未显示类别。

Answer 3

问题1：双倍BMI = 体重KG / (身高METERS * 身高METERS)；

您正在尝试将weightKG除以零，请参阅下面的内联评论

**

import java.util.Scanner;
class BIM 
{
    int weight;
    double weightKG = weight * 0.45359237;
    int height;  // Here value of height is 0 as you are not assigning the value .
    
    double heightMETERS = height * 0.0254; // anything multiplied with 0 height is 0 , heightMETERS value will be 0 
    // The below statement divides weightKG by zero which is infinite and it is not a number 
    double BMI = weightKG / (heightMETERS * heightMETERS); 
    
    public void calculateBMI()
    {    
        System.out.print("The BMI is: " + BMI); // you will sendup printing NaN
    }
}

**

问题2：你永远不会调用bmiCategory方法来打印基于BMI的类别。

如果我要重新格式化和重新排列这段代码，我会这样做。我们仍然可以通过异常处理来改进这一点，但至少我们可以做到这一点。

**

import java.util.Scanner;
class Bmi {

  public double calculateBMI(double weight, double height) {

    double weightKG = weight * 0.45359237;
    double heightMETERS = height * 0.0254;
    double bmi = weightKG / (heightMETERS * heightMETERS);

    return bmi;
  }

  public String bmiCategory(double bmi) {

    if (bmi < 18.5) {
      return "Underweight";
    }

    if (bmi < 25.0) {
      return "Normal";
    }

    if (bmi < 30.0) {
      return "Overweight";
    }

    return "Obese";

  }


}

public class BmiCalculator {

  public static void main(String args[]) {

    Scanner input = new Scanner(System.in);

    System.out.print("Enter weight in pounds: ");
    double weight = input.nextDouble();

    System.out.print("Enter height in inches: ");
    double height = input.nextDouble();

    //validate inputs
    if(height <=0 || weight <=0) {
      System.out.println("The invalid height or weight, "
          + "height and weight should be a positive non zero inputs");
      return;
    }

    Bmi b = new Bmi();
    double bmi = b.calculateBMI(weight, height);
    String category = b.bmiCategory(bmi);
    System.out.println("You belong to "+category+ " category");

  }


}

**

输出：

输入体重（磅）：100

输入高度（以英寸为单位）：6

您属于肥胖类别

输入重量（磅）：0

输入高度（以英寸为单位）：6

无效身高或体重，身高和体重应为正非零输入