Question

I’m writing some code using java.io.BufferedWriter
the first thing I tried was:

    String filename = new String("test.txt");
    Charset charset = new Charset("US-ASCII");
    try {
        BufferedWriter bw = Files.newBufferedWriter(Paths.get(filename), charset);
        bw.write("hello");
    } catch (IOException e) {
        System.out.println(e);
    }

which outputted an empty test.txt
seeing an example, in the following format, I tried:

    String filename = new String("test.txt");
    Charset charset = new Charset("US-ASCII");
    try (BufferedWriter bw = Files.newBufferedWriter(Paths.get(filename), charset)){
        bw.write("hello");
    } catch (IOException e) {
        System.out.println(e);
    }

which outputted a text file with the first line “hello”.
What does this form mean, and why does it work while my first attempt did not?

Answer 1

This is called “try-with-resources” in Java 7, your BufferedWriter will be closed automatically if you fixed it as

    try (BufferedWriter bw = Files.newBufferedWriter(Paths.get("filename"), StandardCharsets.US_ASCII)) {
        bw.write("hello");
    }

See http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html