如何包含转换货币的货币符号？

Question

我尝试在以下link 中更新Java 货币转换器应用程序。 这是代码

   import static javax.swing.JFrame.EXIT_ON_CLOSE;

    public class Main extends JPanel {

    enum Currency {

    USD("United States Dollar"),
    GBR("Great Britain Pound"),
    AUD("Australian Dollar"),
    EUR("Euro");

    private String description;
    Currency(String description) {

        this.description = description;

    }

    @Override public String toString() {
        return this.name() + " - " + this.description;

    }
}
class CurrencyPair {

    private final Currency from;
    private final Currency to;

    public CurrencyPair(Currency from, Currency to) {
        this.from = from;
        this.to = to;
    }

    @Override public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        CurrencyPair that = (CurrencyPair) o;
        if (from != that.from) return false;
        return to == that.to;
    }

    @Override public int hashCode() {
        int result = from.hashCode();
        result = 31 * result + to.hashCode();
        return result;
    }
}

private final Map<CurrencyPair, BigDecimal> exchangeRates = new HashMap<CurrencyPair, BigDecimal>() {{
    put(new CurrencyPair(Main.Currency.USD, Main.Currency.USD), BigDecimal.valueOf(1));
    put(new CurrencyPair(Main.Currency.AUD, Main.Currency.AUD), BigDecimal.valueOf(1));
    put(new CurrencyPair(Main.Currency.EUR, Main.Currency.EUR), BigDecimal.valueOf(1));
    put(new CurrencyPair(Main.Currency.GBR, Main.Currency.GBR), BigDecimal.valueOf(1));

    put(new CurrencyPair(Main.Currency.USD, Main.Currency.GBR), BigDecimal.valueOf(0.75));
    put(new CurrencyPair(Main.Currency.USD, Main.Currency.AUD), BigDecimal.valueOf(1.33));
    put(new CurrencyPair(Main.Currency.USD, Main.Currency.EUR), BigDecimal.valueOf(0.89));

    put(new CurrencyPair(Main.Currency.EUR, Main.Currency.USD), BigDecimal.valueOf(1.12));
    put(new CurrencyPair(Main.Currency.EUR, Main.Currency.AUD), BigDecimal.valueOf(1.49));
    put(new CurrencyPair(Main.Currency.EUR, Main.Currency.GBR), BigDecimal.valueOf(0.85));

    put(new CurrencyPair(Main.Currency.AUD, Main.Currency.USD), BigDecimal.valueOf(0.74));
    put(new CurrencyPair(Main.Currency.AUD, Main.Currency.EUR), BigDecimal.valueOf(0.67));
    put(new CurrencyPair(Main.Currency.AUD, Main.Currency.GBR), BigDecimal.valueOf(0.57));

    put(new CurrencyPair(Main.Currency.GBR, Main.Currency.USD), BigDecimal.valueOf(1.33));
    put(new CurrencyPair(Main.Currency.GBR, Main.Currency.EUR), BigDecimal.valueOf(1.18));
    put(new CurrencyPair(Main.Currency.GBR, Main.Currency.AUD), BigDecimal.valueOf(1.76));

}};

public Main() {
    super(new FlowLayout(FlowLayout.LEADING));

    // Amount
    JTextField amountInput = new JTextField(20);
    JPanel amount = new JPanel();
    amount.add(amountInput);
    amount.setBorder(BorderFactory.createTitledBorder("Enter Amount"));
    add(amount, BorderLayout.CENTER);

    // From
    JPanel from = new JPanel();
    JComboBox fromOptions = new JComboBox(Currency.values());
    from.add(fromOptions);
    from.setBorder(BorderFactory.createTitledBorder("Select currency"));
    add(from, BorderLayout.CENTER);

    // To
    JComboBox toOptions = new JComboBox(Currency.values());
    JPanel to = new JPanel();
    to.add(toOptions);
    to.setBorder(BorderFactory.createTitledBorder("Convert to"));
    add(to, BorderLayout.CENTER);

    // Convert Action
    JLabel convertText = new JLabel();
    JButton convertCmd = new JButton("Convert");
    convertCmd.addActionListener(convertAction(amountInput, fromOptions, toOptions, convertText));
    JPanel convert = new JPanel();
    convert.add(convertCmd);
    convert.add(convertText);
    add(convert);
}

private ActionListener convertAction(
        final JTextField amountInput,
        final JComboBox fromOptions,
        final JComboBox toOptions,
        final JLabel convertText) {

    return new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            // TODO: Needs proper validation
            String amountInputText = amountInput.getText();
            if ("".equals(amountInputText)) { return; }

            // Convert
            BigDecimal conversion = convertCurrency(amountInputText);
            convertText.setText(NumberFormat
                    .getCurrencyInstance(Locale.US)
                    .format(conversion));
        }

        private BigDecimal convertCurrency(String amountInputText) {
            // TODO: Needs proper rounding and precision setting
            CurrencyPair currencyPair = new CurrencyPair(
                    (Currency) fromOptions.getSelectedItem(),
                    (Currency) toOptions.getSelectedItem());
            BigDecimal rate = exchangeRates.get(currencyPair);
            BigDecimal amount = new BigDecimal(amountInputText);
            return amount.multiply(rate);
        }
    };
}


public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.getContentPane().add(new Main());
    frame.setTitle("Currency Thing");
    frame.setSize(500, 500);
    frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}
}

主要问题是.getCurrencyInstance(Locale.US)。美元货币符号出现在所有转换结果中，即使它们与美元不同。

我尝试为货币对创建 if 子句，例如 if(new CurrencyPair(Currency.USD, Currency.USD))，但这不是一个好的代码行。

我想实现一个解决方案，让任何转换结果都有自己的货币。

Answer 1

怎么样：

enum Currency {

    USD("United States Dollar", Locale.US),
    GBP("Great Britain Pound", Locale.UK),
    AUD("Australian Dollar", new Locale("en", "AUS")),
    EUR("Euro", /*here little complicated*/ Locale.FRANCE);

    private final Locale locale;
    private final String description;

    Currency(String description, Locale locale) {
        this.description = description;
        this.locale = locale;
    }
 
    @Override public String toString() {
        return this.name() + " - " + this.description;
    }
    //... getters
}

..通过“语言环境”字段扩展货币。 （或者String currency;）

然后获取并使用它：

 // Convert
 BigDecimal conversion = convertCurrency(amountInputText);
 // fetch (to) locale
 Locale locale = ((Currency) toOptions.getSelectedItem()).getLocale();
 // ... & apply
 convertText.setText(NumberFormat
                .getCurrencyInstance(locale)
                .format(conversion));

我在此解决方案/格式中看到一个（小）问题，即在上述国家/地区的数字格式不一致。 （千位/小数点分隔符将随应用的语言环境而变化）

编辑：

..甚至更糟/更丑陋：一些国家/地区在其货币符号前加上其他国家/地区。

---

更好的方法：

1. 使用 Currency.symbol：

   enum Currency {
   
     USD("United States Dollar", "$"),
     GBP("Great Britain Pound", "£"),
     AUD("Australian Dollar", "AUD"),
     EUR("Euro", "€");
   
     private final String symbol;
    ...
   

2. 引入<Currency, DecimalFormat>的（静态）EnumMap并预填充：

   private static final Map<Currency, DecimalFormat> SYMBOL2FMT
       = new EnumMap<>(Currency.class) {{
       for (Currency c : Currency.values()) {
           put(c, new DecimalFormat("###,###.### " + c.getSymbol()));
       }
   }};
   

3. 将其绑定在一起：

    // Convert ...
    BigDecimal conversion = convertCurrency(amountInputText);
    // fetch (to) symbol
    Currency toCurrency = ((Currency) toOptions.getSelectedItem());
    convertText.setText(SYMBOL2FMT.get(toCurrency).format(conversion));