Question

I have a simple file read and write function.

private void WriteToFile(String filename, String val) {
    PrintWriter outStream = null;
    FileOutputStream fos = null;
    try {
        fos = new FileOutputStream(filename);
        outStream = new PrintWriter(new OutputStreamWriter(fos));
        outStream.print(val);
        outStream.close();
    } catch (Exception e) {
        if (outStream != null) {
            outStream.close();
        }
    }
}

private String ReadFile(String filename) {
    String output = "";
    FileReader fr = null;
    BufferedReader br = null;
    try {
        fr = new FileReader(filename);
        br = new BufferedReader(fr);
        output = br.readLine();
        br.close();
    } catch (Exception e) {
        if (br != null) {
            br.close();
        }
    }

    return output;
}

When building I get:

unreported exception java.io.IOException; must be caught or declared to be thrown
            br.close();
                    ^

Why do I need to catch br.close but it doesn’t complain about WriteToFile’s close()?

Answer 1

Taken from the source code of java.io.PrintWriter:

public void close() {
    try {
        synchronized (lock) {
            if (out == null)
                return;
            out.close();
            out = null;
        }
    }
    catch (IOException x) {
        trouble = true;
    }
}

The IOException was eaten up within the close() method in PrintWriter

From source code of java.io.BufferedReader:

public void close() throws IOException {
    synchronized (lock) {
        if (in == null)
            return;
        in.close();
        in = null;
        cb = null;
    }
}

BufferedReader throws the IOException.

That should answer your question.