How to check for EOF without readLine()?

Question

I have a method that read the next line in a txt file and does something. I have another method that needs to check for EOF as well. The two methods are called receptively within a loop.

method 1:

trace = br.readLine();
   if (trace==null)
       break; // end of file

method 2: I need to check for EOF without using the same technique. Otherwise, it would increment the ptr used for readLine...

Is there any way to accomplish this?

Thanks

check this question: http://stackoverflow.com/questions/2517638/can-i-peek-on-a-bufferedreader and this answer: http://stackoverflow.com/a/2517713/1227804 — user1227804, May 06 '12 at 15:24

score 2 · Answer 1 · edited May 23 '17 at 12:20

Is there any way to accomplish this?

The BufferedReader API doesn't allow you to do this (*). If you really need to do this, you'll need to implement a custom Reader class to do this. I'd start with PushbackReader, add a readLine() method and then implement an eof test method by reading one char and pushing it back.

_{* From reading the answers to Can I peek on a BufferedReader?, it appears that the ready() method might work as an EOF test. However, this is an artifact of the current implementations of ready() in the standard code-base, and is arguably wrong (a bug) according to the javadoc specification of the method.}

score 0 · Accepted Answer · answered May 06 '12 at 15:45

0

You can use

 Scanner sc = new Scanner (file);

and read

 while (sc.hasNext ())

Scanner has a

  sc.readLine ();

method.

answered May 06 '12 at 15:45

user unknown

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This generic answer doesn't begin to solve OP's specific request to check for EOF at two places in the code. – Marko Topolnik May 06 '12 at 16:30
@MarkoTopolnik: Wrong! `Returns true if this scanner has another token in its input. This method may block while waiting for input to scan. The scanner does not advance past any input.` You can invoke the method at different points. – user unknown May 06 '12 at 16:59

Arun Chettoor · Answer 3 · 2012-05-08T06:17:41.150

You can use this format to check as well to avoid EOF exception. Since the buffer size is determined early it will not cause any error to occur.

File myFile = new File("path");
String completeText = "";
FileChannel fc = new FileInputStream(myFile.getAbsoluteFile()).getChannel();
ByteBuffer buffer = ByteBuffer.allocate((int)fc.size());
fc.read(buffer);
Charset charset = Charset.defaultCharset();  
CharsetDecoder decoder = charset.newDecoder();  
CharBuffer charBuffer = decoder.decode(buffer);    
completeText = charBuffer.toString();
buffer.clear();
fc.close();

How to check for EOF without readLine()?

3 Answers3