Pattern.CASE_INSENSITIVE

Question

I am working on a method that accepts a String argument parameter, searches a file for that word and returns a count of the occurrences of that word. I am using Java Regex Pattern and Matcher classes and methods. The way that I have implemented Pattern.CASE_INSENSITIVE does not seem to function correctly. It is still matching on a case sensitive basis.

public int lookup(String wrd) throws IOException, FileNotFoundException, 
{  
    int cnt = 0;     

BufferedReader in = new BufferedReader(new FileReader(this.filename));

    String line = in.readLine();
    while (line != null)
    { 
        Pattern ptn = Pattern.compile(wrd, Pattern.CASE_INSENSITIVE);
        Matcher mtch = ptn.mtch(line);
        if (mtch.find()) {cnt++;}
        line = input.readLine();
    }
    return cnt;
}

Answer 1

You are not scrolling through the lines in the file and only reading first line. There is no reason to use regex, for most languages you can combine toLowerCase() with indexOf() to get a case insensitive position check.

public static void main(String[] args) throws Exception {
  Path p = ...
  String wrd = ...
  System.out.println(totalMatches(p, wrd));
}

private static int totalMatches(Path path, String word) throws IOException {
  try (BufferedReader reader = Files.newBufferedReader(path)) {
    return reader.lines()
        .mapToInt(l -> lineMatches(l, word))
        .sum();
  }
}

private static int lineMatches(String line, String word) {
  int counter = 0, i = 0, found;
  while ((found = line.toLowerCase().indexOf(word.toLowerCase(), i)) >= 0) {
    counter++;
    i = found + 1;
  }
  return counter;
}

Answer 2

Just like I mentioned in the comment fix the mistakes. Here is a bit modified and fixed version of your code. This way seems like everything works:

  public static int lookup(String wrd) throws IOException {
    int cnt = 0;

    BufferedReader in = new BufferedReader(
        new StringReader(new String("word adfasdword avcasf\n asdf WoRd asdfWORDasdf")));

    String line = in.readLine();
    while (line != null) {
      Pattern ptn = Pattern.compile(wrd, Pattern.CASE_INSENSITIVE);
      Matcher mtch = ptn.matcher(line);
      while (mtch.find()) {
        cnt++;
      }
      line = in.readLine();
    }
    return cnt;
  }

  public static void main(String[] args) throws IOException {
    System.out.println(lookup("WORD"));
    System.out.println(lookup("word"));
    System.out.println(lookup("WorD"));
    System.out.println(lookup("worLd"));
  }

Output:

4
4
4
0