Exception Handling and Threading

Checked and unchecked exceptions, try-catch-finally, thread lifecycle, and synchronization.

Exceptions

An exception is an event that disrupts the normal flow of a program.

Types

Checked exceptions — Verified at compile time (e.g., IOException, SQLException).
Unchecked exceptions — Occur at runtime (e.g., ArithmeticException, NullPointerException).
Errors — Serious problems not meant to be caught (e.g., OutOfMemoryError).

Handling Exceptions

try {
    // code that may throw an exception
} catch (ExceptionType e) {
    // handle the exception
} finally {
    // always executes, cleanup code
}

throw — Explicitly throw an exception: throw new Exception("message");
throws — Declare that a method may throw an exception: void method() throws IOException { }

Threading

Thread Lifecycle

A thread passes through these states: New, Runnable, Running, Blocked/Waiting, and Terminated.

Creating Threads

Extending Thread — Override the run() method.
Implementing Runnable — Implement the run() method and pass to a Thread constructor.

Synchronization

The synchronized keyword prevents multiple threads from accessing shared resources simultaneously.

Inter-Thread Communication

wait() — Causes the current thread to wait until notified.
notify() — Wakes up a single waiting thread.
notifyAll() — Wakes up all waiting threads.

Example

// ExceptionThreadDemo.java
// Demonstrates exception handling and threading in Java.

// Exception handling example
class ExceptionDemo {
	public static void main(String[] args) {
		try {
			int a = 5 / 0; // This will cause ArithmeticException
		} catch (ArithmeticException e) {
			// Handle exception
			System.out.println("Exception caught: " + e);
		} finally {
			// Finally block always executes
			System.out.println("Finally block executed");
		}
	}
}

// Thread example
class MyThread extends Thread {
	public void run() {
		// Print thread name
		System.out.println("Thread running: " + getName());
	}
}

public class ExceptionThreadDemo {
	public static void main(String[] args) {
		// Create and start thread
		MyThread t = new MyThread();
		t.start();
	}
}

Full source: examples/12-exceptions-threads/ExceptionThreadDemo.java