java - Is flush() call necessary when using try-with-resources

Question

Will try-with-resources call flush() implicitly?

If it does, in the following code snippet, bw.flush() can be safely removed?

static void printToFile1(String text, File file) {
    try (BufferedWriter bw = new BufferedWriter(new FileWriter(file))) {
        bw.write(text);
        bw.flush();
    } catch (IOException ex) {
        // handle ex
    }
}

ps. I don't see any description about it in official document:

https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html https://docs.oracle.com/javase/8/docs/api/java/lang/AutoCloseable.html

Answer 1

Closeable and AutoCloseable are general-purpose interfaces that do not know anything about flushing. So you can't find any information about it in their documentation - except some words about releasing resources.

A Writer on the other hand is a more specific-purpose abstract class that now knows something about flushing. Some excerpt of the documentation for the method Writer.close():

Closes the stream, flushing it first.

So - yes - when using a writer, a close will always also flush. This basically means that you have to consult the documentation of the concrete classes that you are using when trying to find out what closing really does.