String.format() 抛出 FormatFlagsConversionMismatchException

这段代码在 Java 1.6 中运行良好：

 public static String padLeft(String s, int n)
 {
     if (n <= 0)
         return s;
     int noOfSpaces = n * 2;
     String output;
     noOfSpaces = s.length() + noOfSpaces;
     output = String.format("%1$#" + noOfSpaces + "s", s);
     return output;
 }

但较新的版本（以及其他一些虚拟机实现）会抛出此问题Exception:

java.util.FormatFlagsConversionMismatchException: Mismatched Convertor =s, Flags= #
        at java.util.Formatter$Transformer.transformFromString(Formatter.java:1020)
        at java.util.Formatter$Transformer.transform(Formatter.java:861)
        at java.util.Formatter.format(Formatter.java:565)
        at java.util.Formatter.format(Formatter.java:509)
        at java.lang.String.format(String.java:1961)

有什么解决方法吗？

您要求解决方法；只需使用字符串生成器:

public static String padLeft(String s, int n) {
    if (n <= 0)
        return s;
    int noOfSpaces = n * 2;
    StringBuilder output = new StringBuilder(s.length() + noOfSpaces);
    while (noOfSpaces > 0) {
        output.append(" ");
        noOfSpaces--;
    }
    output.append(s);
    return output.toString();
}