File I/O - JVM's responsibility or the O.S's ?

Question

Hi All,
Try this.
BufferedWriter lWriter = new BufferedWriter(new
FileWriter("sample.txt"));
     lWriter.write("Hi !");
lWriter.newLine();
lWriter.flush();
System.out.println("Finished writing to file");
     /* wait for some time before writing again */
     Thread.sleep(30000);
     System.out.println("Trying to write again");
     lWriter.write("Hi !");
lWriter.newLine();
lWriter.flush();
System.out.println("Finished writing to file again");
There are two write operations in the above code. After the first write operation, change the property of the file to 'Read-only'. Ideally speaking, the second write operation which follows after this should throw a IOException because the file has been made readonly . But no exception is thrown ! Both the write operations are successful (verified by seeing the contents of the file). It seems as though I/O checks are made only initially when the file is opened. In Unix, even if the file is deleted inbetween, there is no exception ! Where is it writing to? Is this a bug in the JVM or in the O/S file system ?

Answer 1

Why should I use another BufferedWriter? The above code was just an example. My program is actually a thread running continously which writes data into a file. I donot want the overhead of creating a new Writer instance for each operation.