CODEWITHSUNDEEP
javaregexstring
CodeMed
CodeMed

Reputation: 9205

escaping +- and -- in java

I want to replace all occurrences of +- with - from a string called myStr in java. I also want to replace all occurrences of -- with + from myStr. The following two lines of code are not accomplishing this in java: 

myStr.replaceAll("\\+-", "-");  
myStr.replaceAll("\\--", "+");

Can anyone show me how to alter these two lines of code to accomplish the desired replacements?

I usually try to avoid regular expressions, but am not sure how to do this operation without them.

Upvotes: 0

Views: 122

Answers (2)

Markus Jarderot
Markus Jarderot

Reputation: 89241

public static String escapePlusMinus(String myStr) {
    Pattern pattern = Pattern.compile("[+-]-");
    Matcher matcher = pattern.matcher(myStr);
    StringBuffer result = new StringBuffer();

    while (matcher.find()) {
        if (matcher.group(0).equals("+-")) {
            matcher.appendReplacement(result, "-");
        }
        else {
            matcher.appendReplacement(result, "+");
        }
    }
    matcher.appendTail(result);

    return result.toString();
}

escapePlusMinus("+-, --, +-, ---+---") ⇒ "-, +, -, +--+"

The last token is matched as:

  1. "--" ⇒ "+"
  2. "-" skipped, since there are not another "-" following it.
  3. "+-" ⇒ "-"
  4. "--" ⇒ "+"

Upvotes: 0

zzzzBov
zzzzBov

Reputation: 179256

You're throwing out the return value of the function. You probably want to use:

myStr = myStr.replaceAll("\\+-", "-").replaceAll("--", "+");

update with additional info from comment:

Be sure to keep the return value of replaceAll.

myStr = myStr.replaceAll("\\+-", "-");

and later

myStr = myStr.replaceAll("--", "+");

Upvotes: 5

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