Java try with resources on parameters

Question

this is a stupid question, but I can't figure it out. Do I need to close Object passed as parameters inside a try with resources ?

here it is an example:

StringWriter sw = new StringWriter();
try (PrintWriter pw = new PrintWriter(sw)) {
    ...
}

Do I need to call

sw.close();

after the try block ? or does it close automatically all the Autocloseable objects passed as parameters ?

Answer 1

The implicit invocation of close on your PrintWriter will actually close the underlying Writer as well.

See following example:

StringWriter sw = new StringWriter() {
        @Override
        public void close() throws IOException {
            super.close();
            System.out.println("closed");
        }
};
try (PrintWriter pw = new PrintWriter(sw)) {};

Output

closed