Converting a dynamic string variable to a regex expression for string.match()?

Question

I have a string variable being passed down to the method check() called 'letters' (Say). The string is therefore going to be dynamic.

The method requires checking if the words passed separately in an arraylist contain only the characters contain within 'letters'.

I have the following within my loop, with the word string changing each time as the loop iterates through the array.

word = wordArray.get(i);

if ((word.length() <= letters.length()) && (word.matches(letters))
{
    // Do something.
}

The string.matches() seems the way to go, however I'm having issues figuring out how I can use the letters string variable as an expression which the matches used, given the above code does not work.

My thoughts are that I may need to add certain expression characters, or perhaps escape the letters string? (I've played around with this though with no luck) Could anyone advise as to how I can ensure the word can only contain characters from the string variable 'letters'?

Thanks

Niklas B. · Accepted Answer · 2014-02-27 18:47:51Z

1

You can do

Pattern p = Pattern.compile("[" + Pattern.quote(letters) + "]*");

and then later:

if (word.length() <= letters.length() && p.matcher(word).matches());

answered Feb 27, 2014 at 18:47

Niklas B.

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1 Comment

Niklas B. Over a year ago

@Error-404: You could also roll your own algorithm using a lookup or hash table. It's probably much faster to do it that way.

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