Java File I/O: Why do I always get an I/O exception?

Question

I am trying to write to a file and then read from that same file. The output is "Error: I/O exception". Meaning that the program is catching the IOException.

public class fileIO {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        try
        {
            File file = new File("io.txt");
            BufferedReader read = new BufferedReader(new FileReader(file));
            BufferedWriter write = new BufferedWriter(new FileWriter(file));

            String needs = "This is going to the file";
            write.write(needs);

            String  stuff = read.readLine();
            while(stuff != null)
            {
                System.out.println(stuff);
                stuff = read.readLine();
            }

        }
        catch(IOException e)
        {
            System.out.println("Error: I/O Exception");
        }
        catch(NullPointerException e)
        {
            System.out.println("Error: NullPointerException");
        }
    }
}'

Look at the stacktrace, and you should add it to the question. Can be simply done by doing `e.printStackTrace()` in the catch block. — mkobit, Nov 19 '14 at 22:54
Printing the stack trace would tell you more about what went wrong. Just let `main` throw the exception instead of catching it. — Jörn Horstmann, Nov 19 '14 at 22:54
My guess goes for the fact that he is writing AND reading into THE SAME FILE at the SAME TIME. — EpicPandaForce, Nov 19 '14 at 22:56

user3424612 · Accepted Answer · 2014-11-19T23:16:32.393

You cannot read from and write to the file at the same time, this will throw an IOException. You should close anything that has access to the file before trying to access it with something else. Invoking the close() method on BufferedWriter before trying to access the file with BufferedReader should do the trick.

EDIT: Also, as others have mentioned, you can use e.printStackTrace() to see where an exception has occurred in your program, which greatly helps when debugging.

EDIT: As zapl clarified, this is the case for some file systems, including Windows, but not all. It was my assumption that you were using a file system that restricts this as it seemed like the most likely problem.

Oppression57 · Answer 2 · 2014-11-20T00:09:48.167

I moved the BufferedReader to after where I closed the the BufferedWriter and that did the trick. thanks for the help.

public class fileIO {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    try
    {
        File file = new File("io.txt");
        BufferedWriter write = new BufferedWriter(new FileWriter(file));

        String needs = "This is going to the file";
        write.write(needs);
        write.close();

        BufferedReader read = new BufferedReader(new FileReader(file));

        String  stuff = read.readLine();
        while(stuff != null)
        {
            System.out.println(stuff);
            stuff = read.readLine();
        }
        read.close();
    }
    catch(IOException e)
    {
        System.out.println("Error: I/O Exception");
        e.printStackTrace();
    }
    catch(NullPointerException e)
    {
        System.out.println("Error: NullPointerException");
        e.printStackTrace();
    }
}

}

Java File I/O: Why do I always get an I/O exception?

2 Answers2