When are readers/writers/streams identified as being open?

Question

I am creating an abstract binding class for a Reader and Writer where the user doesn't have to reference each one individually.

Example: I have a FileStream which inside of it houses both a FileReader and FileWriter .

The question I have refers to optimizing the class. I know I can't have two streams opened simultaneously due to concurrency, however I need to initialize them somewhere without having data leaks all over the place.

Are streams/readers/writers classified as being open, as soon as you initialize them, or are the 'pipes' only opened once the first read/write begins? I'm looking at the JavaDoc and don't see anything here about when the streams actually open up...

For those who do not understand what I am asking (ignoring try-catch blocks):

// does my reader become OPEN here?
BufferedReader br = new BufferedReader(new FileReader("foobar.txt"));

// or here, now that I have performed the first operation.
br.readLine();

Answer 1

They are open as soon as you construct them. There is no 'open' operation, so they are already open.

Discussion:

new FileInputStream(...) and new FileOutputStream(...) open the file, as they throw IOExceptions about it. Practically every other input or output stream extends FilterInput/OutputStream, with a FileInput/OutputStream as its delegate (including socket input/output streams as a matter of fact). The FileInput/OutputStream is created first in any such stack, ergo it is already open before the decorator streams, ergo they are already open too.

ByteArrayInput/OutputStreams and StringReader/Writer don't need opening at all.

Answer 2

Alternative solution: forget about re-inventing the wheel.

Java has a class that is specifically designed to allow for reading and writing to the same file: java.io.RandomAcessFile

So, if you have to wrap around... Use that class, instead of combining two other things that were never intended to be combined!