Find a string (or a line) in a txt File Java

Question

let's say I have a txt file containing:

john
dani
zack

the user will input a string, for example "omar" I want the program to search that txt file for the String "omar", if it doesn't exist, simply display "doesn't exist".

I tried the function String.endsWith() or String.startsWith(), but that of course displays "doesn't exist" 3 times.

I started java only 3 weeks ago, so I am a total newbie...please bear with me. thank you.

Ruchira Gayan Ranaweera · Accepted Answer · 2013-12-06T07:58:35.960

6

Just read this text file and put each word in to a List and you can check whether that List contains your word.

You can use Scanner scanner=new Scanner("FileNameWithPath"); to read file and you can try following to add words to List.

 List<String> list=new ArrayList<>();
 while(scanner.hasNextLine()){
     list.add(scanner.nextLine()); 

 }

Then check your word is there or not

if(list.contains("yourWord")){

  // found.
}else{
 // not found
}

BTW you can search directly in file too.

while(scanner.hasNextLine()){
     if("yourWord".equals(scanner.nextLine().trim())){
        // found
        break;
      }else{
       // not found

      }

 }

edited Dec 06 '13 at 07:58

answered Dec 06 '13 at 07:22

Ruchira Gayan Ranaweera

34,993
17
75
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why put it into a list instead of checking the line directly and breaking the loop when a match was found? Like this, each time you read in the whole file, which size we don't know. Could be very inefficient.... – Blub Dec 06 '13 at 07:26
@EdgarBoda your idea is there too – Ruchira Gayan Ranaweera Dec 06 '13 at 07:29
that last method, where I can search directly inside the file, how to break the loop when the line is found? it's displaying: not found 4 times, then found, then not found until the end of the file – user3040333 Dec 06 '13 at 07:37
@user3040333 just put a `break` – Ruchira Gayan Ranaweera Dec 06 '13 at 07:58
@Ruchira already tried that, it somehow cancels the if statement, so it's now showing not found wether the string exists or not – user3040333 Dec 06 '13 at 08:19
@user3040333 try with debugger – Ruchira Gayan Ranaweera Dec 06 '13 at 08:21
@Ruchira same problem and here's the debugger console Listening on javadebug User program running User program finished – user3040333 Dec 06 '13 at 08:28

score 1 · Answer 2 · answered Dec 06 '13 at 07:22

1

use String.contains(your search String) instead of String.endsWith() or String.startsWith()

eg

 str.contains("omar");

answered Dec 06 '13 at 07:22

Prabhakaran Ramaswamy

25,706
10
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score 1 · Answer 3 · answered Dec 06 '13 at 07:24

You can go other way around. Instead of printing 'does not exist', print 'exists' if match is found while traversing the file and break; If entire file is traversed and no match was found, only then go ahead and display 'does not exist'.

Also, use String.contains() in place of str.startsWith() or str.endsWith(). Contains check will search for a match in the entire string and not just at the start or end.

Hope it makes sense.

Hitman · Answer 4 · 2013-12-06T08:13:49.547

Read the content of the text file: http://www.javapractices.com/topic/TopicAction.do?Id=42

And after that just use the textData.contains(user_input); method, where textData is the data read from the file, and the user_input is the string that is searched by the user

UPDATE

public static StringBuilder readFile(String path) 
 {       
        // Assumes that a file article.rss is available on the SD card
        File file = new File(path);
        StringBuilder builder = new StringBuilder();
        if (!file.exists()) {
            throw new RuntimeException("File not found");
        }
        BufferedReader reader = null;
        try {
            reader = new BufferedReader(new FileReader(file));
            String line;
            while ((line = reader.readLine()) != null) {
                builder.append(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

       return builder;
    }

This method returns the StringBuilder created from the data you have read from the text file given as parameter.

You can see if the user input string is in the file like this:

int index = readFile(filePath).indexOf(user_input);
        if ( index > -1 )
            System.out.println("exists");

instead of textData, should I put the name of the file? for example File file = new File(); then put "file" instead of textData ? — user3040333, Dec 06 '13 at 07:47

score 0 · Answer 5 · answered Sep 19 '18 at 06:40

You can do this with Files.lines:

try(Stream<String> lines = Files.lines(Paths.get("...")) ) {
    if(lines.anyMatch("omar"::equals)) {
  //or lines.anyMatch(l -> l.contains("omar"))
        System.out.println("found");
    } else {
        System.out.println("not found");
    }
}

Note that it uses the UTF-8 charset to read the file, if that's not what you want you can pass your charset as the second argument to Files.lines.

Find a string (or a line) in a txt File Java

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