Java Regex - To parse function name and argument name - throws PatternSyntaxException: Unclosed Character

Question

Here is the regex i used to extract the function name

Regex

^(\w+(\s+)?){2,}\([^!@#$+%^]*\)

Code

final static String functionNameRegex = "^(\\w+(\\s+)?){2,}\\([^!@#$+%^]*\\)";
final static String functionString = "public void render(int screenNo, String infoText){}";


final Pattern fnPattern = Pattern.compile(functionNameRegex, Pattern.CASE_INSENSITIVE | Pattern.COMMENTS);
final Matcher fnMatcher = fnPattern.matcher(functionString);

while (fnMatcher.find()) {
       System.out.println("Full match: " + fnMatcher.group(0));
       for (int i = 1; i <= fnMatcher.groupCount(); i++) {
             System.out.println("Group " + i + ": " + fnMatcher.group(i));
       }
}

But, it throws PatternSyntaxException. Not sure what's causing the problem here, as i am able to get the desired output in other languages.

Traces:

Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed character class near index 30
^(\w+(\s+)?){2,}\([^!@#$+%^]*\)
                              ^
    at java.util.regex.Pattern.error(Pattern.java:1955)
    at java.util.regex.Pattern.clazz(Pattern.java:2548)
    at java.util.regex.Pattern.sequence(Pattern.java:2063)
    at java.util.regex.Pattern.expr(Pattern.java:1996)
    at java.util.regex.Pattern.compile(Pattern.java:1696)
    at java.util.regex.Pattern.<init>(Pattern.java:1351)
    at java.util.regex.Pattern.compile(Pattern.java:1054)
    at TestRegex.main(TestRegex.java:28)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

New to regex, assist me out in rechanging this regex to identify and group the parameter names.

Wiktor Stribiżew · Accepted Answer · 2017-05-02 10:40:10Z

4

You compile the regex with Pattern.COMMENTS and you have a # symbol inside the pattern. You need to escape it, else, it denotes the start of a comment.

Use

final static String functionNameRegex = "^(\\w+(\\s+)?){2,}\\([^!@\\#$+%^]*\\)";

See the Java demo.

Also, consider changing (\\w+(\\s+)?){2,} to (\\w+(?:\\s+\\w+)+) if you plan to match 2 or more space separated words (it will work much faster) (Group 1 will still hold the value before the parentheses).

answered May 2, 2017 at 10:40

Wiktor Stribiżew

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2 Comments

surendhar_s Over a year ago

Thanks. that helped. please provide input on re-changing this regex to capture the parameter names.

Wiktor Stribiżew Over a year ago

@surendhar_s See ideone.com/rujQfw, sorry, I am just not sure what you need.

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