Threads

Threads

1. What Is a Thread? (beginner)

Thread = mini-program inside program (own stack, shared Heap!). Main + workers run together (music + download + chat!). Process = house; threads = family sharing kitchen (Heap!) with own rooms (stacks!).

2. Why Threads? (exam reasons!)

Responsive UI (button works while file loads!), faster multi-core (4 cores → 4× work!), background tasks (music while typing!).

3. First Thread (two ways — exam both!)

// WAY 1: extends Thread (simple, one-shot!)
class Hi extends Thread {
    public void run() { for (int i = 0; i < 3; i++) System.out.println("hi " + i); }
}
// WAY 2: implements Runnable (flexible — preferred! can still extend!)
class Hello implements Runnable {
    public void run() { for (int i = 0; i < 3; i++) System.out.println("hello " + i); }
}
new Hi().start(); // start() (NOT run()!) → new thread!
new Thread(new Hello()).start(); // wrap Runnable!
// Output interleaves! (hi/hello mixed — schedular decides order!)

4. start() vs run() (THE trap!)

start() = new thread (parallel!). run() = normal call (same thread, NO parallel!). Beginners calling run() get sequential (no magic!).

5. Exam Points

• Define + two ways program — 7 marks, very frequent.
• start vs run — 5 marks, all-time favourite trap.