Question

Lets say I have a string = “hello”. how do i open a text file and check if hello exists in that text file?

contents of the text file:

hello:man:yeah

i tried using the code below. Is it file reader only reads the first line? i need it to check all lines to see if hello exists, and then if it does, take “man” from it.

try {
    BufferedReader in = new BufferedReader(new FileReader("hello.txt"));
    String str;
    while ((str = in.readLine()) != null) {
        System.out.println(str);
    }
} catch (IOException e) {
    System.out.println("Error.");
}

Answer 1

If hello:man:yeah is one line in your file, then your code is working right. readLine() will read a line until a newline is found (one line in this case).

If you just want to see if it’s in the file, then you could do something like this:

 String str;
 boolean found = false;
 while ((str = in.readLine()) != null) {
       if(str != null && !found){
         found = str.contains("hello") ? true : false;
       }
    }

If you need to do a whole word search, you’ll need to use a regular expression. Surrounding your search text with \b will do the whole word search. Here’s a snippet (Note, StringUtils comes from Apache Commons Lang):

    List<String> tokens = new ArrayList<String>();
    tokens.add("hello");

    String patternString = "\\b(" + StringUtils.join(tokens, "|") + ")\\b";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(text);

    while (matcher.find()) {
        System.out.println(matcher.group(1));
    }

Of course, if you don’t have multiple tokens, you can just do this:

String patternString = "\\bhello\\b";