Java Buffered Writer

Question

File file = new File("result.csv");
FileWriter fw = new FileWriter(file.getAbsoluteFile());
BufferedWriter bw = new BufferedWriter(fw);

What happens if we do not close the buffered writer object after the write completion? I mean what if we miss bw.close()?

Answer 1

If you open many files, and if you don't close them, your operating system will be unable to open any more files after a while.

Also, while your BufferedWriter has not been garbage collected, the file it was writing to will remain open as far as your operating system is concerned. If that's Windows, you will not be able to delete the file until the file handle is closed, either by the BufferedWriter finally being garbage collected or by the JVM exiting.

• BufferedWriter.close() flushes the buffer to the underlying stream, so if you forget to flush() and don't close, your file may not have all the text you wrote to it.

• BufferedWriter.close() also closes the wrapped Writer. When that's a FileWriter, this will ultimately close a FileOutputStream and tell the OS that you're done writing to the file.

• The garbage collector will automatically call close(), not on the BufferedWriter or the wrapped FileWriter, but on the FileOuputStream. So the OS will be happy, but you have to wait for the GC.

• However, you always want to release OS resources as soon as you no longer need them. This goes for open files, database connections, print queues ... anything. Trust me on this one.

• BufferedWriter.close() does clear up the internal character buffer, so that memory will be available for garbage collection, even while the BufferedWriter itself remains in scope.

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