Question

我正在尝试使用散列图编写Java单元转换程序。每次我尝试运行我的代码时，convert()都会抛出异常，我不知道为什么会这样做？这里发生了什么？请给出提示，而不是完整的答案。谢谢！

FWIW，输入遵循格式3 meters to inches。

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Conversions {
    static private ArrayList<Map<String, Double>> conversions = new ArrayList<Map<String, Double>>();

    Map<String, Double> conversion;

    { // length
        conversion = new HashMap<String, Double>();
        conversion.put("kilometers", 1e-3);
        conversion.put("meters", 1.0);
        conversion.put("angstroms", 1e-10);
        conversion.put("inches", 39.3701);
        conversion.put("yards", 1.09361);
        conversion.put("attoparsecs", 32.4077929);
        conversion.put("miles", 0.000621371);
        conversions.add(conversion);
    }

    { // weight
        conversion = new HashMap<String, Double>();
        conversion.put("kilograms", 1.0);
        conversion.put("grams", 1000.0);
        conversion.put("pounds", 2.20462);
        conversion.put("ounces", 35.274);
        conversion.put("slugs", 0.0685217649);
        conversion.put("hogsheads of Beryllium", 440.7);
        conversions.add(conversion);
    }

    public static double convert(double value, String unitFrom, String unitTo) throws Exception {
        for (int i = 0; i < conversions.size(); i++) {
            if (conversions.get(i).containsKey(unitFrom) && conversions.get(i).containsKey(unitTo)) {
                return value * conversions.get(i).get(unitTo) / conversions.get(i).get(unitFrom);
            }
        }
        throw new Exception(value + " " + unitFrom + " can't be converted to " + unitTo);
    }

    private static void parse(String line) {
        String[] splitStrings = line.split("\\s+");
        double value = Double.parseDouble(splitStrings[0]);
        try {
            double convertedValue = convert(value, splitStrings[1], splitStrings[3]);
            System.out.format("%f %s is %f %s%n", value, splitStrings[1], convertedValue, splitStrings[3]);
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        parse(scanner.nextLine());
        scanner.close();
    }
}

Answer 1

提示：如果我是你，我会在方法转换循环中放入一个断点，并检查这种情况是否适用：

if (conversions.get(i).containsKey(unitFrom) && conversions.get(i).containsKey(unitTo)) {

HashMap单元转换程序无法识别密钥

1 个答案: