问题
Language is Java. What does the %1$# mean in...
static String padright (String str, int num) {
return String.format("%1$#" + num + "str", str);
}
In the Java API, String.format() is used in this way:
public static String format(String format, Object... args)
So I think %1$# is a format specifier.
%[flags][width][.precision][argsize]typechar is the template.
- 1 is a flag?
- $ is the width?
- # is the precision?
- num is the argsize?
- "str" is the typechar?
Is that right?
回答1:
Template:
%[argument_index$][flags][width][.precision]conversion
The optional argument_index is a decimal integer indicating the position of the argument in the argument list. The first argument is referenced by "1$", the second by "2$", etc.
The optional flags is a set of characters that modify the output format. The set of valid flags depends on the conversion.
The optional width is a decimal integer indicating the minimum number of characters to be written to the output.
The optional precision is a non-negative decimal integer usually used to restrict the number of characters. The specific behavior depends on the conversion.
The required conversion is a character indicating how the argument should be formatted. The set of valid conversions for a given argument depends on the argument's data type.
%1$ refers to the first substitution. In this case the string str.
# is flag which says the result should use a conversion-dependent alternate form.
http://download.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html
来源：https://stackoverflow.com/questions/5762836/what-does-1-mean-when-used-in-string-format-java