Question

我是java新手，我正在开发一个计算用户BMI的程序。我无法弄清楚为什么我的while循环不能用于我的InputMismatchException。第一次它会说它不正确，但如果你第二次输入它会崩溃。任何帮助将不胜感激。

import java.util.*;

public class W8
{
   public static void main (String[] args) 
   {
      //Utilities
      Scanner in = new Scanner(System.in);

      //Variables
      double height = 0.0;
      double weight = 0.0;
      boolean error = false;
      double bmi = 0.0;  

      do 
      {
         try 
         {
            error = false;
            while (height <=0)
            {
               System.out.println("Enter height in inches:");
               height = in.nextDouble();
            }
         } 
         catch (InputMismatchException e) 
         {
            in.nextLine();
            System.out.println("Invalid inches value. Must be a decimal number.");
            System.out.println("Re-enter height in inches:");
            height = in.nextDouble();
            error = true;
         } 
      }while (error);

      do
      {
         try
         {
            error = false;
            while (weight <=0)
            {
            System.out.println("Enter weight in pounds:");
            weight = in.nextDouble();
            }
         } 
         catch (InputMismatchException e)
         {

            in.nextLine();
            System.out.println("Invalid pounds value. Must be a decimal number.");
            System.out.println("Re-enter weight in pounds:");
            weight = in.nextDouble();
            error = true;
         } 
      }while (error);

      //bmi calculation
      bmi = (weight/(height*height))*703;

      //Outputs
      System.out.println("Height = " +height+".");
      System.out.println("Weight = " +weight+".");
      System.out.println("Body mass index = " +bmi+ ".");
   }
}

Answer 1

这在Java中称为自动类型提升。以下是类型促销的基本规则

类型促销规则

扩展转换不会丢失有关值的大小的信息。例如，将int值分配给double变量。这种转换是合法的，因为双倍比整数更宽。 Java的扩展转换是

从一个字节到一个短，一个int，一个long，一个float或一个double

从short到int，long，float或double

从char到int，long，float或double

从int到long，float或double

从长到浮动或双重

从浮动到双重

double是最宽的原始类型，正是由于这些统治，当你在程序中输入整数时，它们被提升为double

Answer 2

试试这个：

public static void main（String [] args）{

    // Utilities
    Scanner in = new Scanner(System.in);

    // Variables
    double height = 0.0;
    double weight = 0.0;
    boolean error = false;
    double bmi = 0.0;
    System.out.println("Enter height in inches:");
    while (height <= 0) {
        try {
            height = in.nextDouble();
        } catch (InputMismatchException e) {
            height = -1;
            System.out
                    .println("Invalid inches value. Must be a decimal number.");
            System.out.println("Re-enter height in inches:");
            in.nextLine();
            error = true;
        }
    }

    System.out.println("Enter weight in inches:");
    while (weight <= 0) {
        try {
            weight = in.nextDouble();
        } catch (InputMismatchException e) {
            weight = -1;
            System.out
                    .println("Invalid inches value. Must be a decimal number.");
            System.out.println("Re-enter weight in inches:");
            in.nextLine();
            error = true;
        }
    }
    // bmi calculation
    bmi = (weight / (height * height)) * 703;

    // Outputs
    System.out.println("Height = " + height + ".");
    System.out.println("Weight = " + weight + ".");
    System.out.println("Body mass index = " + bmi + ".");
}

do while循环，InputMismatchException

2 个答案: