Why can't java recognize this Regular Expression?

Question

I wrote this Regular Expression:

((http):\\/\\/\\S*\\.(jpg|gif|png))

This Regex should find every image link in a string

And as you can see it work fine if you click the link below.

http://rubular.com/r/FYwP8Aprdb

But when I then paste it into java and escape all of the back- slashes and call replaceAll(regex, string);

The program can't find anything?

String regex = "((http):\\/\\/\\S*\\.(jpg|gif|png))";
boxText.replaceAll(regex, "**$0**");

The code above should get every image in a string and then capsulate it in $0 But upon running the program and testing, nothing happens.

public class SSCCE {

public static void main(String[] args) {

    String boxText = "http://www.desibucket.com/db2/01/26039/26039.jpg";

    String regex = "((http):\\/\\/\\S*\\.(jpg|gif|png))";
    boxText.replaceAll(regex, "**$1**");        

    System.out.println(boxText);
}

/* output

  http://www.desibucket.com/db2/01/26039/26039.jpg

 */

}

My assumption is that I've escaped the regex incorrectly, but I'm not sure. Any ideas?

Answer 1

字符串是不可变的 ：表达式匹配，但永远不会将值重新分配给replaceAll的结果

boxText = boxText.replaceAll(regex, "**$1**");