Java 接收无穷大值

我试图做一个单位转换程序，但我一直接受无穷大的值。我不确定我需要修复哪里，因为它不会给我错误。我只测试了oz到ml，以确保我做得正确，但我得到的答案是无穷大

UnitConverter.java：

public class UnitConverter {

    final double oz_TO_ml = 29.5735; 
    final double gal_TO_g = 3.78541;
    final double lb_TO_kg = 0.453592;
    final double inc_TO_mm = 25.4;//Inc is inches
    final double ft_TO_cm = 30.48;
    final double mi_TO_km = 1.60934;

    double factor;

    public UnitConverter(String unit) {
        if (unit.equals("oz")) {
            factor = oz_TO_ml;
        } else if (unit.equals("gal")) {    
            factor = gal_TO_g;
        } else if (unit.equals("lb")) {     
            factor = lb_TO_kg;
        }
    }

    public double toOz(double amount) {
        return (amount * factor);
    }

    public double fromOz(double amount) {
        return (amount / factor);
    }

    public double toMl(double amount) {
        return (amount * factor);
    }

    public double fromMl(double amount) {
        return (amount / factor);
    }
}

import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Convert from: ");
        String fromUnit = in.nextLine();

        System.out.print("Convert to: ");
        String toUnit = in.nextLine();

        UnitConverter from = new UnitConverter(fromUnit);
        UnitConverter to = new UnitConverter(toUnit);

        System.out.print("Value ");
        double val = in.nextDouble();

        double oz = from.toOz(val);
        double converted = to.fromOz(oz);

        System.out.println(val + " " + fromUnit + " = " + converted + " " + toUnit);
    }
}

Convert from: oz
Convert to: ml
Value 12

12.0 oz = Infinity ml

Calculator.java：

public class UnitConverter {

    final double oz_TO_ml = 29.5735; 
    final double gal_TO_g = 3.78541;
    final double lb_TO_kg = 0.453592;
    final double inc_TO_mm = 25.4;//Inc is inches
    final double ft_TO_cm = 30.48;
    final double mi_TO_km = 1.60934;

    double factor;

    public UnitConverter(String unit) {
        if (unit.equals("oz")) {
            factor = oz_TO_ml;
        } else if (unit.equals("gal")) {    
            factor = gal_TO_g;
        } else if (unit.equals("lb")) {     
            factor = lb_TO_kg;
        }
    }

    public double toOz(double amount) {
        return (amount * factor);
    }

    public double fromOz(double amount) {
        return (amount / factor);
    }

    public double toMl(double amount) {
        return (amount * factor);
    }

    public double fromMl(double amount) {
        return (amount / factor);
    }
}

import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Convert from: ");
        String fromUnit = in.nextLine();

        System.out.print("Convert to: ");
        String toUnit = in.nextLine();

        UnitConverter from = new UnitConverter(fromUnit);
        UnitConverter to = new UnitConverter(toUnit);

        System.out.print("Value ");
        double val = in.nextDouble();

        double oz = from.toOz(val);
        double converted = to.fromOz(oz);

        System.out.println(val + " " + fromUnit + " = " + converted + " " + toUnit);
    }
}

Convert from: oz
Convert to: ml
Value 12

12.0 oz = Infinity ml

样本输入：

public class UnitConverter {

    final double oz_TO_ml = 29.5735; 
    final double gal_TO_g = 3.78541;
    final double lb_TO_kg = 0.453592;
    final double inc_TO_mm = 25.4;//Inc is inches
    final double ft_TO_cm = 30.48;
    final double mi_TO_km = 1.60934;

    double factor;

    public UnitConverter(String unit) {
        if (unit.equals("oz")) {
            factor = oz_TO_ml;
        } else if (unit.equals("gal")) {    
            factor = gal_TO_g;
        } else if (unit.equals("lb")) {     
            factor = lb_TO_kg;
        }
    }

    public double toOz(double amount) {
        return (amount * factor);
    }

    public double fromOz(double amount) {
        return (amount / factor);
    }

    public double toMl(double amount) {
        return (amount * factor);
    }

    public double fromMl(double amount) {
        return (amount / factor);
    }
}

import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Convert from: ");
        String fromUnit = in.nextLine();

        System.out.print("Convert to: ");
        String toUnit = in.nextLine();

        UnitConverter from = new UnitConverter(fromUnit);
        UnitConverter to = new UnitConverter(toUnit);

        System.out.print("Value ");
        double val = in.nextDouble();

        double oz = from.toOz(val);
        double converted = to.fromOz(oz);

        System.out.println(val + " " + fromUnit + " = " + converted + " " + toUnit);
    }
}

Convert from: oz
Convert to: ml
Value 12

12.0 oz = Infinity ml

输出：

public class UnitConverter {

    final double oz_TO_ml = 29.5735; 
    final double gal_TO_g = 3.78541;
    final double lb_TO_kg = 0.453592;
    final double inc_TO_mm = 25.4;//Inc is inches
    final double ft_TO_cm = 30.48;
    final double mi_TO_km = 1.60934;

    double factor;

    public UnitConverter(String unit) {
        if (unit.equals("oz")) {
            factor = oz_TO_ml;
        } else if (unit.equals("gal")) {    
            factor = gal_TO_g;
        } else if (unit.equals("lb")) {     
            factor = lb_TO_kg;
        }
    }

    public double toOz(double amount) {
        return (amount * factor);
    }

    public double fromOz(double amount) {
        return (amount / factor);
    }

    public double toMl(double amount) {
        return (amount * factor);
    }

    public double fromMl(double amount) {
        return (amount / factor);
    }
}

import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Convert from: ");
        String fromUnit = in.nextLine();

        System.out.print("Convert to: ");
        String toUnit = in.nextLine();

        UnitConverter from = new UnitConverter(fromUnit);
        UnitConverter to = new UnitConverter(toUnit);

        System.out.print("Value ");
        double val = in.nextDouble();

        double oz = from.toOz(val);
        double converted = to.fromOz(oz);

        System.out.println(val + " " + fromUnit + " = " + converted + " " + toUnit);
    }
}

Convert from: oz
Convert to: ml
Value 12

12.0 oz = Infinity ml

---

您的

UnitConverter

类构造函数只知道3个单位：

oz

、

gal

和

lb

。如果使用其中一个进行实例化，它将正确分配因子并能够转换单位，如下所示：

public UnitConverter(String unit) {
    if (unit.equals("oz")) {
        factor = oz_TO_ml;
    } else if (unit.equals("gal")) {    
        factor = gal_TO_g;
    } else if (unit.equals("lb")) {     
        factor = lb_TO_kg;
    }
}

但是，在计算器类中，您有以下行：

UnitConverter from = new UnitConverter(fromUnit);
UnitConverter to = new UnitConverter(toUnit);

double converted = to.fromOz(oz);

如果使用示例输入运行程序，则从is

oz

到is

ml

。但是，如果您使用单位

ml

实例化

UnitConverter

，那么该因子设置为什么？根据您的构造函数，它从未设置，因此它保留默认值

0.0

稍后，您可以调用此行：

UnitConverter from = new UnitConverter(fromUnit);
UnitConverter to = new UnitConverter(toUnit);

double converted = to.fromOz(oz);

这将运行

fromOz

方法

public double fromOz(double amount) {
    return (amount / factor);
}

除以系数，即

0.0

。这是无限输出的来源

正如另一个答案所说，执行此计算不需要两个

UnitConverter

对象。这个系数在盎司和毫升之间的转换是正确的，所以这个计算器代码就足够了

import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.print("Convert from: ");
        String fromUnit = in.nextLine();

        UnitConverter from = new UnitConverter(fromUnit);

        System.out.print("Value ");
        double val = in.nextDouble();

        double result = from.toMl(val);

        System.out.println(val + " " + fromUnit + " = " + result + " ml.");
    }
}

如果希望保留当前的计算器代码，则需要在

UnitConverter

构造函数中为ml（

1.0

）的scalefactor添加一个条件。然而，我认为这种方法是有缺陷的，因为当你尝试在盎司和英寸之间转换时会发生什么？这种转换毫无意义，但您的体系结构不会阻止它

public UnitConverter(String unit)
{ 
       if (unit.equals("oz")) 
       { 
           factor = oz_TO_ml; 
        } else if (unit.equals("gal")) 
        { 
            factor = gal_TO_g; 
        } else if (unit.equals("lb")) 
        { factor = lb_TO_kg; 
        } 
  }

如果通过“ml”，则因子将为零

您的设计目前需要其中两个，但您实际上只需要一个，因为“oz”拥有进行转换所需的一切

忽略行输入代码中的toUnit，只使用fromUnit

编辑：我将向您展示另一种方式，它只支持一个转换来显示粗略的设计。注意，方法调用现在是静态的，因为您只需要它们的一个实例

UnitConverter.java

public class UnitConverter 
{

  private static final double oz_TO_ml = 29.5735;    

  public static double convert(String fromType, String toType,double amount) throws IllegalArgumentException
  {
      if (fromType.equals("oz") && toType.equals("ml"))
      {
          return (amount * oz_TO_ml);
      }
      else
      {
          throw new IllegalArgumentException("The combination of converting " + fromType + " to " + toType + " is not supported");
      }
  }    
}

Calculator.java：

import java.util.Scanner;

public class Calculator {

public static void main(String[] args) {

    Scanner in = new Scanner(System.in);

    System.out.print("Convert from: ");
    String fromUnit = in.nextLine();

    System.out.print("Convert to: ");
    String toUnit = in.nextLine();

    System.out.print("Value ");
    double val = in.nextDouble();

    System.out.println(val + " " + fromUnit + " = " + UnitConverter.convert(fromUnit,toUnit,val) + " " + toUnit);
}

---

}用一初始化因子变量。默认值为0的java将原语double

   class UnitConvertor {

    final double oz_TO_ml = 29.5735; 
    final double gal_TO_g = 3.78541;
    final double lb_TO_kg = 0.453592;
    final double inc_TO_mm = 25.4;//Inc is inches
    final double ft_TO_cm = 30.48;
    final double mi_TO_km = 1.60934;

    double factor=1;//initialize with 1

---

但我仍然不确定，如果用户输入为“ml”，您使用的检查是什么。

您在运行时键入了什么？系统输出的结果是什么statement@immibis我运行它并在oz中输入，当它要求convert from:时，然后输入ml表示conver to:和12表示value，您的程序使用什么转换因子表示“ml”？将“oz”转换为“ml”意味着什么？这不取决于物质吗？你说的通过“ml”是什么意思？im现在有点丢失UnitConverter to=新的UnitConverter（toUnit）；哦，好的。我怎么修复它呢？我试着忽略了toUnit，它给了我一个语法error@Jay我想他是在建议你退后一步，从一开始就努力去理解这个问题。没有人能在不了解问题是什么的情况下成功地解决问题。一旦你真正理解了这个问题，解决这个问题的正确方法就会更容易找到。请点击我的答案旁边显示为“禁用”的回答标志。我会的，但它不允许我这样做。说我没有必要的15个名声。@jay不用担心快乐的Codingthanks！你帮我省了很多时间试图解决这个问题。@jay这不是一个真正的答案，所以不要太激动，它所做的只是隐藏了你对代码如何工作的中间理解，它涵盖了一些严重的基本设计错误伟大的答案，它很好地描述了问题，并且有更好的解决方案