Regex (Java): How do I replace "||" with "| |" repeatedly

Question

If I have a string of pipe-delimited data:

123456|abcd|||65464|hgfhgf

How can I replace any occurrance of || with: | |?

So it would end up looking like this:

123456|abcd| | |65464|hgfhgf

I tried using the simple Java expression:

delimString.replaceAll("\\\|\\\|", "| |");

but that only replaced the first occurrence:

123456|abcd| ||65464|hgfhgf

So I need something to make it repeat (greedily I think).

Answer 1

String resultString = subjectString.replaceAll("\\|(?=\\|)", "| ");

The regex explained without Java's double backslashes:

\|   # Match a literal |
(?=  # only if it's followed by
 \|  # another literal |.
)    # End of lookahead assertion

You could even go wild and replace the empty space between two pipes with a space character:

String resultString = subjectString.replaceAll("(?<=\\|)(?=\\|)", " ");

Answer 2

The problem is here that the match position is already past the 2nd | you replaced, so it does not count. You'll have to use a while loop to do this.

Answer 3

I agree with Ingo - a loop solution is more lines of code but easier to understand (at least it doesn't have to be explained ;) ):

String test = "abc|def||ghi|||jkl";

StringBuilder result = new StringBuilder();
char previous = 0;
for (char c:test.toCharArray()) {
  if (c == '|' && previous == '|')
    result.append(" ");
  result.append(c);
  previous = c;
}

System.out.println(result);