Just read the docs.

here is the read method docs http://docs.oracle.com/javase/7/docs/api/java/io/FileInputStream.html#read()

public int read() throws IOException Reads a byte of data from this input stream. This method blocks if no input is yet available.

Specified by: read in class InputStream

Returns: the next byte of data, or -1 if the end of the file is reached.

That int is a your next set of bytes data. Now , here are the answers.

1) When you assign a char to an int, it denotes it's ascii number to the int.

If you are interested, here us the list of chars and their ascii codes https://www.cs.cmu.edu/~pattis/15-1XX/common/handouts/ascii.html

2)-1 if the end of the file is reached. So that's a check to data exists or not.

3)When you send an ascii code to print writer, it's prints that corresponding char to the file.

The problem with my code in an infinite loop of reading and writing. I can't find a solution or a concept for this problem.

There's a number of problems with your code:

• The file will be treated as empty after the FileOutputStream gets instantiated because you've set append flag to false. End method read() will always return -1 because there's no content to read.

• Condition is incorrect and method read() and only because of that control enters the loop and EOF (-1) is being repeatedly written into the file. If you fixed the condition to (m = in.read()) != -1, the loop would be ignored because the file is blank from the start.

• If you would do both: fix the condition and change the append flag to true then you would get another flavor of infinite loop. All the contents of the file will be successfully read and repeatedly appended to the file.

So at any condition, reading and writing simultaneously to the same file isn't a good idea.

One important note in regard to exception handling.

Because there's no catch block in your code snippet, I assume that you've added a throws to the main() - it's not a nice idea. Methods close() in your code will be invoked only in case of successful execution, but if exception occur resources will never get released.

Instead, I suggest you to make use of try with resources. That will provide an implicit finally block for you that will take care of closing the resources regardless whether exception occurred or not (now your invocations of close() will not get executed in case of exception). Another option is to declare finally block explicitly, and close the resources inside it.

Try with resource is more concise and cleaner way to ensure that resources will get released.

Also consider wrapping both streams with buffered high-level streams to improve performance. It'll significantly reduce the number of time your application will need to access the file system.

    try (var in = new BufferedInputStream(new FileInputStream("source.txt"));
         var out = new BufferedOutputStream(new FileOutputStream("destination.txt", false))) {

        int next; // a subsequent byte that has been read from the source
        while ((next = in.read()) != -1) {
            out.write(next);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }