华氏到摄氏的转换只产生 0.0 和 -0.0 [英] Fahrenheit to Celsius conversion yields only 0.0 and -0.0

问题描述

我正在阅读 Java 方法书的第 8 章(方法、构造函数和字段)，但我的一个练习有问题.

I'm on the 8th chapter (Methods, Constructors, and Fields) of my Java methods book and I'm having a problem with one of my exercises.

提供的代码是Temperature.java

The provided code is Temperature.java

  import java.awt.*;
  import java.awt.event.*;
  import javax.swing.*;
  import java.text.DecimalFormat;

  public class Temperature extends JApplet
   implements ActionListener {
      private JTextField displayF, displayC;
      private static DecimalFormat displayFormat = new DecimalFormat("0.0");

      public void init() {
          Container c = getContentPane();
          c.setBackground(Color.white);
          c.setLayout(new GridLayout(2, 2, 10, 0));

          c.add(new JLabel("  Fahrenheit:"));
          c.add(new JLabel("  Celsius:"));

          displayF = new JTextField(6);
          displayF.setBackground(Color.yellow);
          displayF.addActionListener(this);
          c.add(displayF);

          displayC = new JTextField(6);
          displayC.setBackground(Color.yellow);
          displayC.addActionListener(this);
          c.add(displayC);
      }

      public void actionPerformed(ActionEvent e) {
          String s;
          double degrees;
          FCConverter fc = new FCConverter();

          if ((JTextField) e.getSource() == displayF) {
              s = displayF.getText().trim();
              degrees = Double.parseDouble(s);
              fc.setFahrenheit(degrees);
              degrees = fc.getCelsius();
              displayC.setText(displayFormat.format(degrees));
          } else {
              s = displayC.getText().trim();
              degrees = Double.parseDouble(s);
              fc.setCelsius(degrees);
              degrees = fc.getFahrenheit();
              displayF.setText(displayFormat.format(degrees));
          }
      }
  }

然后我应该编写和测试 FCConverter.java我想出了:

And from there I'm supposed to write and test FCConverter.java I've come up with:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.DecimalFormat;

public class FCConverter
{
  private double Celsius;
  private double Fahrenheit;
  public double setFahrenheit (double degrees)
  {
      Celsius = (degrees - 32) * (5 / 9);
      return 0;
  }
  public double getCelsius ()
  {
      return Celsius;
  }
  public double setCelsius (double degrees)
  {
  Fahrenheit = (degrees * 9 / 5 + 32);
          return 0;
  }
  public double getFahrenheit ()
  {
      return Fahrenheit;
  }
}

这在风格方面可能很糟糕，但我只是想获得一些通过编译器的工作代码(因此我相当肯定可以以更时尚的方式规避return 0;").

It's probably horrendous in terms of style, but I just wanted to get some working code that got past the compiler (hence the "return 0;"s which I'm fairly certain can be circumvented in a much more fashionable manner).

我想知道的是，当我在 appletviewer 或浏览器形式中测试时，摄氏到华氏的转换工作正常，但华氏到摄氏的转换仅产生 0.0 和 -0.0.我不明白出了什么问题，因为我设计的部分看起来相当对称.不应该是两种转换方法都有效吗?

What I want to know is, when I test this in appletviewer or in browser form, the Celsius to Fahrenheit conversion works fine, but the Fahrenheit to Celsius conversion yields only 0.0 and -0.0. I don't understand what's wrong since the part I've designed seems fairly symmetrical. Shouldn't it be the case that both or neither conversion method works?

推荐答案

问题好像是 5/9.它们被视为一个整数，5/9 是 0.something 是 0 作为整数.所以无论如何 * 0 = +-0 :)

The problem seems to be 5/9. They are seen as an integer, and 5/9 is 0.something which is 0 as an integer. So whatever * 0 = +-0 :)

在数字后放置一个d"，(5d/9d) 迫使编译器将它们视为双倍.

Place a "d" after the numbers, (5d/9d) forcing the compiler to consider them doubles.

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