Android : Issue on appending a file in android

I am creating an android application which reads and writes data to a file in the location /sdcard/ReadandWrite/.when i writing to that file it does not write in append mode.please help me to solve this.Here is my code.

private File openfile() {
    File sdCard = Environment.getExternalStorageDirectory();
    File dir = new File (sdCard.getAbsolutePath() + "/ReadandWrite");
    dir.mkdirs();
    File file = new File(dir, "myfile.txt");
    file.setWritable(true);
    if(file.exists())
    {
        file.canRead();
        file.setWritable(true);

    }
    else {
        try {
            file.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return file;
}

private void writetofile() {


    try {
        File file=openfile();
        OutputStreamWriter myOutWriter =
                new OutputStreamWriter(new FileOutputStream(file));
        myOutWriter.append(text.getText());

        myOutWriter.close();
        myOutWriter.close();
        Toast.makeText(getBaseContext(),
                "Done writing SD 'mysdfile.txt'",
                Toast.LENGTH_SHORT).show();
    } catch (Exception e) {
        Toast.makeText(getBaseContext(), e.getMessage(),
                Toast.LENGTH_SHORT).show();
    }