try-with-resources and suppressed exceptions

Any AutoCloseable declared in the try header is closed automatically, in reverse order, even on exception — and a failure during close is attached to the primary exception rather than replacing it.

try (InputStream in = Files.newInputStream(src);
     OutputStream out = Files.newOutputStream(dst)) {
    in.transferTo(out);
}   // out closed first, then in — both guaranteed

What the old form got wrong

InputStream in = null;
try {
    in = Files.newInputStream(src);
    read(in);                       // throws IOException  <- the real cause
} finally {
    if (in != null) in.close();     // also throws          <- this one wins
}

The exception from close() replaces the one you care about. try-with-resources keeps the first and records the second:

catch (IOException e) {
    for (Throwable s : e.getSuppressed()) { /* the close failure */ }
}

Details

Resources must be effectively final; since Java 9 an existing final variable can be named directly in the header.
close() should be idempotent, because nothing prevents a second call.
A finally block still runs after all resources are closed, if you need one.

2 questions on this concept Drill it