Single Tasking Using Threads

Single Tasking Using Threads

1. What It Means (beginner — odd-sounding!)

Single tasking with threads = ONE worker thread + main (sequential handoff!). Used to learn lifecycle: main waits (join) while worker finishes. Like relay: one runs at a time!

2. Code — Main Waits for Worker (join!)

class Bill implements Runnable {
    public void run() {
        System.out.println("bill: adding items...");
        try { Thread.sleep(1000); } catch (InterruptedException e) {}
        System.out.println("bill: total=150");
    }
}
public static void main(String[] args) throws InterruptedException {
    Thread t = new Thread(new Bill());
    t.start();   // worker starts
    t.join();    // MAIN WAITS (single-task feel — ordered!)
    System.out.println("main: pay done!"); // prints AFTER bill!
}
// Output order guaranteed: bill lines → pay done! (join forces!)

3. Why? (exam viva!)

Teaches start + join + order control. Real single-tasking needs no threads — this pattern shows coordination (background + wait!).

4. Traps

• join() throws InterruptedException (handle/throws!).
• Without join, main may end first (worker orphan — output jumbled!).
• join(1000) waits max 1s (timed version!).

5. Exam Points

• join program + order guarantee — 5 marks, frequent.
• With vs without join output — 3 marks, trap.