CODEWITHSUNDEEP
javabufferedreader
AussieJeffProbst
AussieJeffProbst

Reputation: 571

Using BufferedReader.readLine() in a while loop properly

So I'm having an issue reading a text file into my program. Here is the code:

try {
    InputStream fis = new FileInputStream(targetsFile);
    BufferedReader br = new BufferedReader(new InputStreamReader(fis));

    //while(br.readLine()!=null){
    for (int i = 0; i < 100; i++) {
        String[] words = br.readLine().split(" ");
        int targetX = Integer.parseInt(words[0]);
        int targetY = Integer.parseInt(words[1]);
        int targetW = Integer.parseInt(words[2]);
        int targetH = Integer.parseInt(words[3]);
        int targetHits = Integer.parseInt(words[4]);
        Target a = new Target(targetX, targetY, targetW, targetH, targetHits);
        targets.add(a);
    }
    br.close();
} catch (Exception e) {
    System.err.println("Error: Target File Cannot Be Read");
}

The file I am reading from is 100 lines of arguments. If I use a for loop it works perfectly. If I use the while statement (the one commented out above the for loop) it stops at 50. There is a possibility that a user can run the program with a file that has any number of lines, so my current for loop implementation won't work.

Why does the line while(br.readLine()!=null) stop at 50? I checked the text file and there is nothing that would hang it up.

I don't get any errors from the try-catch when I use the while loop so I am stumped. Anyone have any ideas?

Upvotes: 28

Views: 197917

Answers (8)

Andreas Kielkopf
Andreas Kielkopf

Reputation: 11

If you are using a newer version of Java (like 21), you can use instanceof to make the while() work. You also can use try() with your Closable resource

 try (FileInputStream fis=new FileInputStream(targetsFile);
           BufferedReader br=new BufferedReader(new InputStreamReader(fis));) {
     while (br.readLine() instanceof String line) {
        String[] words=line.split(" ");
        int targetX=Integer.parseInt(words[0]);
        int targetY=Integer.parseInt(words[1]);
        int targetW=Integer.parseInt(words[2]);
        int targetH=Integer.parseInt(words[3]);
        int targetHits=Integer.parseInt(words[4]);
        Target a=new Target(targetX, targetY, targetW, targetH, targetHits);
        targets.add(a);
     }
  } catch (Exception e) {
     System.err.println("Error: Target File Cannot Be Read");
  }

instanceof works great here, because it calls readLine, does check for null (to feed the while) and gives the String-Object a name. instanceof does check for null

Upvotes: 1

Chirag Shah
Chirag Shah

Reputation: 51

Concept Solution:br.read() returns particular character's int value so loop continue's until we won't get -1 as int value and Hence up to there it prints br.readLine() which returns a line into String form.

    //Way 1:
    while(br.read()!=-1)
    {
      //continues loop until we won't get int value as a -1
      System.out.println(br.readLine());
    }

    //Way 2:
    while((line=br.readLine())!=null)
    {
      System.out.println(line);
    }

    //Way 3:
    for(String line=br.readLine();line!=null;line=br.readLine())
    {
      System.out.println(line);
    }

Way 4: It's an advance way to read file using collection and arrays concept How we iterate using for each loop. check it here http://www.java67.com/2016/01/how-to-use-foreach-method-in-java-8-examples.html

Upvotes: 5

Gene Parmon
Gene Parmon

Reputation: 105

In addition to the answer given by @ramin, if you already have BufferedReader or InputStream, it's possible to iterate through lines like this:

reader.lines().forEach(line -> {
    //...
});

or if you need to process it with given order:

reader.lines().forEachOrdered(line -> {
    //...
});

Upvotes: 4

ramin
ramin

Reputation: 968

In case if you are still stumbling over this question. Nowadays things look nicer with Java 8:

try {
  Files.lines(Paths.get(targetsFile)).forEach(
    s -> {
      System.out.println(s);
      // do more stuff with s
    }
  );
} catch (IOException exc) {
  exc.printStackTrace();
}

Upvotes: 12

Mona Jalal
Mona Jalal

Reputation: 38155

You can use a structure like the following:

 while ((line = bufferedReader.readLine()) != null) {
            System.out.println(line);
        }

Upvotes: 20

ramin
ramin

Reputation: 968

also very comprehensive...

try{
    InputStream fis=new FileInputStream(targetsFile);
    BufferedReader br=new BufferedReader(new InputStreamReader(fis));

    for (String line = br.readLine(); line != null; line = br.readLine()) {
       System.out.println(line);
    }

    br.close();
}
catch(Exception e){
    System.err.println("Error: Target File Cannot Be Read");
}

Upvotes: 50

AussieJeffProbst
AussieJeffProbst

Reputation: 571

Thank you to SLaks and jpm for their help. It was a pretty simple error that I simply did not see.

As SLaks pointed out, br.readLine() was being called twice each loop which made the program only get half of the values. Here is the fixed code:

try{
        InputStream fis=new FileInputStream(targetsFile);
        BufferedReader br=new BufferedReader(new InputStreamReader(fis));
        String words[]=new String[5];
        String line=null;
        while((line=br.readLine())!=null){
            words=line.split(" ");
            int targetX=Integer.parseInt(words[0]);
            int targetY=Integer.parseInt(words[1]);
            int targetW=Integer.parseInt(words[2]);
            int targetH=Integer.parseInt(words[3]);
            int targetHits=Integer.parseInt(words[4]);
            Target a=new Target(targetX, targetY, targetW, targetH, targetHits);
            targets.add(a);
        }
        br.close();
    }
    catch(Exception e){
        System.err.println("Error: Target File Cannot Be Read");
    }

Thanks again! You guys are great!

Upvotes: 5

SLaks
SLaks

Reputation: 887365

You're calling br.readLine() a second time inside the loop.
Therefore, you end up reading two lines each time you go around.

Upvotes: 31

Related Questions