Java error while using replaceAll("+-", "-")

Question

I'm trying to use String.replaceAll but I'm getting an error:

Here is my code:

public static String signSimplify (String str) {
    String strr = str.replaceAll("--", "+");
    String strr2 = strr.replaceAll("-+", "-");
    String strr3 = strr2.replaceAll("+-", "-");
    return strr3;
}

And, when executed, I get the following error:

Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '+' near index 0
+-
^
    at java.util.regex.Pattern.error(Unknown Source)
    at java.util.regex.Pattern.sequence(Unknown Source)
    at java.util.regex.Pattern.expr(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.util.regex.Pattern.<init>(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.lang.String.replaceAll(Unknown Source)
    at fr.genius.main.Main.signSimplify(Main.java:108)
    at fr.genius.main.Main.calcTrinome(Main.java:88)
    at fr.genius.main.Main.main(Main.java:69)`

I don't understand why I can't use a replaceAll("+-", "-") but I can when + and - are inversed.

Answer 1

If you don't want or need regular expressions, just use replace() instead of replaceAll() and it will work like you expected.