try-with-resources

try-with-resources

Any AutoCloseable can be managed by try-with-resources; the compiler writes the finally-cleanup for you — in reverse acquisition order:

static String firstLine(Path p) throws IOException {
    try (BufferedReader r = Files.newBufferedReader(p)) {
        return r.readLine();
    }   // r.close() guaranteed, even on exception
}

Two resources close right-to-left:

try (var in = openInput(); var out = openOutput(in)) {
    ...
}   // out closed first, then in — the dependency order

Suppressed exceptions: if the body throws AND close() throws, the close exception is attached to the body exception (getSuppressed()), never lost. With hand-written finally, the close exception would replace the body exception — swallowing the real failure.

The sandbox cannot touch real files, so this course exercises AutoCloseable with in-memory resources — the semantics are identical.