I was trying to replace concatenation symbol '+' with '||' in given multi-line script, however it seems that java regex just replaces 1 occurrence, instead of all.
String ss="A+B+C+D";
Matcher mm=Pattern.compile("(?imc)(.+)\\s*\\+\\s*(.+)").matcher(ss);
while(mm.find())
{
System.out.println(mm.group(1));
System.out.println(mm.group(2));
ss=mm.replaceAll("$1 \\|\\| $2");
}
System.out.println(ss); // Output: A+B+C||D, Expected: A||B||C||D
The reason you only replace one element, is because you match the entire line. The regular expression you use "(?imc)(.+)\\s*\\+\\s*(.+)", matches anything (.+) until the end, then reverts, so it can match the rest \\s*\\+.... So basically your group 1 is .+ almost everything, but the last + and beyond. Therefore replaceAll can only match once, and will terminate after that one replacement.
What you need is a replacement that finds + optionally wrapped in spaces:
Pattern.compile("(?imc)\\s*\\+\\s*");
This should match all you want to match, and does not match the entire line, but only your replacement character.
You could just use:
ss = ss.replaceAll("\\+", "||")
as @ernest_k has pointed out. If you really want to continue using a matcher with iteration, then use Matcher#appendReplacement with a StringBuffer:
String ss = "A+B+C+D";
Matcher mm = Pattern.compile("\\+").matcher(ss);
StringBuffer sb = new StringBuffer();
while (mm.find()) {
mm.appendReplacement(sb, "||");
}
mm.appendTail(sb);
System.out.println(sb);
$1 and $2 etc. are only available in the second parameter replacement to String#replaceAll. The approach you are taking does not make much sense, because the loop means you are iterating over the input, and replaceAll is yet iterating again. Follow the pattern I gave in the second part of my answer if you want to iterate with a regex pattern.I thing maybe we would just need a simple string replace:
import java.util.regex.Matcher;
import java.util.regex.Pattern;
final String regex = "\\+";
final String string = "A+B+C+D";
final String subst = "||";
final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
final Matcher matcher = pattern.matcher(string);
final String result = matcher.replaceAll(subst);
System.out.println(result);
This link on the right panel explains your original expression. The first capturing group does match between one and unlimited times, as many times as possible, thus it would not work here. If we would have changed them to (.+?), it would have partially worked, yet still unnecessary.
ss.replaceAll("\\+", "||")?