regex - including strings: java

Question

I am trying to print out lines from a file which match a particular pattern in java. I am using the Pattern class for doing this.

I tried putting the patter as "[harry]" so that every line which has "harry" gets printed out. But pattern always evaluates to false. My assumption is that the regex pattern I am entering is a string.

My code is as follows:

try {

      BufferedReader br = new BufferedReader(new FileReader("test.txt"));
      Pattern p = Pattern.compile("harry");
      String str = null;
      try {
        while((str = br.readLine())!=null){
          Matcher match = p.matcher(str);
          boolean b = match.matches();
          if(b){
            System.out.println(str);
          }
        }
      } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }

Please help. I am not understanding where the code is breaking. I am trying different pattern matches but is this the correct way to do it?

Thanks

Answer 1

If you are only interested in matching substrings (as opposed to more complex patterns), you do not need to use regular expressions at all.

if (str.contains(substring))

But I assume you were just simplifying the question.

Answer 2

The problem is Matcher.matches must match the entire string. Either use Matcher.find, or change your pattern to allow leading and trailing characters.

Pattern p = Pattern.compile(".*harry.*");