Thread Methods

The Thread class exposes critical API methods that allow controlling thread execution, yielding CPU resource, blocking for other threads, and coordinating thread shutdown via interruption.

Key Thread Methods

• sleep(long millis): Pauses execution of the current thread. Crucially, it does NOT release any monitor locks.
• join(): Suspends the calling thread until the target thread finishes execution.
• yield(): Suggests to the OS scheduler that the current thread is willing to yield its current CPU time slice. The scheduler is free to ignore this hint.
• interrupt(): Sends a signal to the target thread to stop what it is doing. If the thread is blocked in sleep(), join(), or wait(), it wakes up and throws an InterruptedException, clearing its interrupt flag. If it is running, the interrupt flag is set to true.

Code Walkthrough

This program demonstrates how to interrupt a thread that is sleeping and how to handle the interruption gracefully.

public class ThreadMethodsDemo {
    public static void main(String[] args) throws InterruptedException {
        Thread worker = new Thread(() -> {
            while (!Thread.currentThread().isInterrupted()) {
                System.out.println("Working...");
                try {
                    Thread.sleep(1000); // Throws exception if interrupted while sleeping
                } catch (InterruptedException e) {
                    System.out.println("Interrupted during sleep. Cleaning up...");
                    // Re-set interrupt flag to propagate status
                    Thread.currentThread().interrupt(); 
                }
            }
            System.out.println("Worker thread exiting cleanly.");
        });
worker.start();
        Thread.sleep(2500); // Let worker run for a bit
        System.out.println("Requesting interruption...");
        worker.interrupt(); // Signal worker thread
        worker.join(); // Wait for worker to exit
        System.out.println("Main thread done.");
    }
}

Interview-Relevant Information