Exceptions, I/O and Concurrency Basics

Exceptions

Know the hierarchy and the rules:

• Checked exceptions (IOException) must be caught or declared.
• Unchecked exceptions (RuntimeException and subclasses like NullPointerException) need not be.
• finally runs whether or not an exception was thrown; catch blocks must be ordered most-specific first.

try (var reader = new BufferedReader(new FileReader("f.txt"))) {
    return reader.readLine();          // try-with-resources auto-closes
} catch (IOException e) {
    return "error";
}

Try-with-resources

Any resource implementing AutoCloseable can go in the try(...) header and is closed automatically – the exam expects you to recognise this pattern.

Concurrency basics

You should understand creating threads, the Runnable interface, and why shared mutable state needs synchronisation:

Runnable task = () -> System.out.println("running");
new Thread(task).start();

Know that thread scheduling is not guaranteed and that synchronized / concurrent collections protect shared data.

Key points

• Checked exceptions must be handled or declared; unchecked need not be.
• finally always runs; order catch blocks specific-to-general.
• Try-with-resources auto-closes AutoCloseable resources.
• Understand threads, Runnable, and why shared state needs synchronisation.