finally and try-with-resources

finally runs after the try (and any matching catch) whether or not an exception was thrown, and even after a return. It is skipped only if the JVM stops (System.exit, a crash) or the thread never finishes.

Manual cleanup in finally is verbose and easy to get wrong (null checks, and an exception from close() can hide the original one). try-with-resources (Java 7+) closes any AutoCloseable automatically, in reverse order of opening, and keeps the original exception — exceptions from close() are attached as suppressed:

try (BufferedReader in = Files.newBufferedReader(Path.of("marks.csv"));
     BufferedWriter out = Files.newBufferedWriter(Path.of("report.txt"))) {
    String line;
    while ((line = in.readLine()) != null) out.write(line.toUpperCase() + "\n");
} catch (IOException e) {
    System.err.println("Could not process file: " + e.getMessage());
}   // out is closed, then in - no finally needed

One trap worth mentioning: a return inside finally overrides the try's return value and swallows any exception, so never return from finally.