Java Regular expression with variable string

Question

I want to find the occurrences of all the words in a ListArray comparing it with a String. So far, I am able to do it as a for loop, where I store all the possible combinations and run them using a matches i.e.

        for(String temp_keywords: keywords){
        final_keywords_list.add(" "+ temp_keywords+ " ");
        final_keywords_list.add(" "+ temp_keywords+".");
        final_keywords_list.add(" "+ temp_keywords+ ",");
        final_keywords_list.add(" "+ temp_keywords+ "!");
        final_keywords_list.add(" "+ temp_keywords+ "/");
        final_keywords_list.add(" "+ temp_keywords+ "?");
    }
    for (String temp_keywords : final_keywords_list) {
            String add_space = temp_keywords.toLowerCase();
            p = Pattern.compile(add_space);
            m = p.matcher(handler_string);
            int count = 0;
            while (m.find()) {
                count += 1;
            }

However, I want to remove the manual addition for the combinations and do a regex. I've seen examples of words with regex but how do I add a variable string to the regex? Sorry, I am a beginner java learner.

you aren't using final_keywords_list in your code. Are you supposed to match values with temp_keywords or with final_keywords_list? — Eyal Schneider
– Eyal Schneider, Commented Mar 25, 2014 at 6:39
Yes, sorry, I will have to do that. Sorry, this is a part of a large code. I'll edit it now! — P R
– P R, Commented Mar 25, 2014 at 6:43

Eyal Schneider · Accepted Answer · 2014-03-25 06:59:31Z

1

Is this what you need?

String inputString = ....
String[] keywords = ....

StringBuilder sb = new StringBuilder();
for(String keyword: keywords)
  sb.append("(?<= )").append(keyword).append("(?=[ .,!/?])").append("|");
sb.setLength(sb.length() - 1); //Removes trailing "|". Assumes keywords.size() > 0.

Pattern p = Pattern.compile(sb.toString());
Matcher m = p.matcher(inputString);
int count = 0;
while (m.find())
  count++;

It creates a single regex, compiles it, and then counts the matches.

edited Mar 25, 2014 at 6:59

answered Mar 25, 2014 at 6:47

Eyal Schneider

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5 Comments

P R Over a year ago

Thank you! StringBuilder is what I was looking for! I was simply trying to concat the strings and the regex part and it obviously didn't work. I shall read up on StringBuilder.

P R Over a year ago

Sorry, spaces between words of keywords? As in, if the keyword was 'bread and'?

Eyal Schneider Over a year ago

@PR: Before my fix, it didn't count correctly " hello world " as 2. Now I'm using positive lookahead/lookbehind, so it works fine.

Eyal Schneider Over a year ago

Please note that when the input string terminates with one of your words it will also fail to count it, but that's also true with your original solution so I assumed you don't need it.

P R Over a year ago

Awesome. I didn't think of that drawback! And true, I don't need it for my code. Thank you.

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