Question

I’m trying to write a method that will scan a string for certain characters, and report back which of them (if any) were found:

// Special characters are ~, #, @, and *
// If text == "Hello~Clarice, you're s#o ambitious", then this
// method should return a string == "~#". If no special characters
// found, return null. If the same special character occurs 2+ times,
// ignore it and do not return strings with duplicate special chars, like
// "##@***", etc. --> just "#@*".
public String detectAndGetSpecialCharacters(String text) {
    Pattern p = Pattern.compile("[~#@*]");
    Matcher m = pattern.matcher(text);

    String specialCharactersFound = null;
    if(m.find()) {
        // ???
    }

    return specialCharactersFound;
}

I’ve completed the detect portion of this method, but am struggling to find an efficient/elegant way of using the Matcher to tell me which special characters were found, and furthermore, to concatenate them all together (removing duplicates!) and return them. Thanks in advance!

Answer 1

Rather than using a String, you can use a StringBuilder, and append each matched character to it, if it is not already there: –

StringBuilder builder = new StringBuilder();
while (m.find()) {
    String str = m.group();
    if (!builder.toString().contains(str)) {
        builder.append(str);
    }
}

// And finally
return builder.toString();

---

Another way would be to maintain a Set<String>, and keep on adding matched characters to it. It will automatically remove duplicates. And then you can merge the values of the Set to form a String using Apache Commons StringUtils#join() method. Or you can simply iterate over the Set and append each string to a StringBuilder object. Whatever way you like would fit.