在与数字相邻的Java正则表达式中使用反向引用

Question

I want to use a regexp replace with back references If the target string is something like:

"$1 123"

every thing works fine. but if I want a target string like:

"$1123"

It wont work.

in perl, you can use

"${1}123"

To distinguish between the back reference an adjacent numbers - is there a java equivalent?

EDIT

If have time stamps of the format

YYYYMMDDHHMMSS

like:

20130811123000

and I want to reset the hours, minutes, and seconds to get

20130811000000

What I would like to do is

String newstring = timestamp.replaceFirst("(\\d{8}))\\d{6}","${1}000000");

Answer 1

您需要将替换指定为：

"$1\\123"

Answer 2

$12 would refer to the 12th group if it exists, or 1st group if there are less than 12 backreferences.

So, in $1123 $1 if only one group captured, $11 if more than 11 groups captured and so on

reference

Answer 3

It seems an escape works.

See this case:

String input = "abcd";
System.out.println(input.replaceAll("(a)bcd(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?", "$1123"));
System.out.println(input.replaceAll("(a)bcd(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?(e)*?", "$1\\123"));

Output:

23
a123

In this case I have an ambiguity between back-referenced group 1 and back-referenced group 11. In the 1st print I don't escape the back-reference, so group 11 is likely to be interpreted, and it's empty. In the 2nd print I escape the replacement after the back-reference to group 1.