正则表达式 - 捕获花括号之间的增量数字

Question

I have a piece of code that tries to repeatedly match a pattern with an incremented index inside a loop:

for(int count = 0; count < args.length; count++) {
        message.replaceFirst("^\\{" + count + "\\d}$", args[count]);
    }

What I want to be able to do is replace occurrences of {0}, {1} and so on in the message string with those in args. But try as I might, I simply cannot get the pattern to match. I am no regex expert, but I have tried a variety of regex combinations based on other questions here. I also tried using the replace method in StringUtils to no avail. Can anyone offer any suggestions?

Answer 1

Do not use a regex at all. You know your search string beforehand and it is constant (ie you can build it from constant strings plus variable count ) and thus there is no need to incorporate regular expressions.

Answer 2

The ^ and $ characters are anchors. They match the beginning and end of the string. That expression will only match if the entire String is nothing but {\\\\d} . I don't think they need to be there at all.

Also, Strings are immutable in java, the correct usage would be message = message.replaceAll(blah);

Answer 3

Try this regex:

String pattern = "^\\{\\d+\\}$";

Explanation:

1. From the start of the string get a {
2. Then get as many digits as possible
3. Until a } is reached in the end of the string

Example:

String s = "{12}";
String pattern = "^\\{\\d+\\}$";
String s2 = s.replaceFirst(pattern, "9");

System.out.println(s2);

Outputs:

9

This should be fairly easy to apply to your code.