java.util.UnknownFormatConversionException : Conversion = '2'

Question

我不断收到此转换错误:

> Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = '2'
    at java.util.Formatter.checkText(Unknown Source)
    at java.util.Formatter.parse(Unknown Source)
    at java.util.Formatter.format(Unknown Source)
    at java.util.Formatter.format(Unknown Source)
    at java.lang.String.format(Unknown Source)
    at BookTest.main(BookTest.java:40)

这是我遇到问题的代码:

double total = 0;

    for (int i=0; i<quantityArray.length; i++)
    {
        message += String.format("%s %s $%2.f", bookArray[i].getTitle(), bookArray[i].getIsbn(), bookArray[i].calculateCharge(quantityArray[i]));
        total += bookArray[i].calculateCharge(quantityArray[i]);
    }

    message += String.format("Total is: $%2.f", total);
    JOptionPane.showMessageDialog(null, message);

Answer 1

Syntax是:

%[argument_index$][flags][width][.precision]conversion

如您所见，.必须后跟一个精度值。

您的值 (%2.f) 无效。
如果要输出为$123.45，则需要翻转2和.:%.2f