Multithreading Interview Questions

title: Multithreading Interview Questions description: Java Multithreading and Concurrency interview questions

Q1. Thread kya hai? Process se kya fark hai?

• Process — Independent program execution, alag memory space
• Thread — Process ka lightweight sub-unit, shared memory

Q2. Thread create karne ke tarike?

1. Thread class extend karna
2. Runnable interface implement karna
3. Callable interface (return value + exception)
4. ExecutorService (recommended)

Q3. Thread life cycle kya hai?

New → Runnable → Running → Blocked/Waiting → Terminated

Q4. synchronized keyword kya karta hai?

Ek time par sirf ek thread us method/block ko execute kar sakti hai. Race condition rokta hai.

Q5. wait(), notify(), notifyAll() kya hain?

• wait() — Thread lock release karke wait karta hai
• notify() — Ek waiting thread ko wake up karta hai
• notifyAll() — Sabhi waiting threads ko wake up karta hai
• Ye sirf synchronized block mein use hote hain

Q6. Deadlock kya hai? Kaise rokein?

Deadlock: Do threads ek-doosre ka lock wait kar rahe hain, dono stuck.

Rokne ke tarike:

• Lock order consistent rakho
• tryLock() use karo
• Timeout set karo

Q7. volatile keyword kya hai?

Variable ki value hamesha main memory se read hogi, cache se nahi. Visibility guarantee deta hai but atomicity nahi.

Q8. Thread.sleep() vs wait() difference?

Q9. ExecutorService kya hai?

Thread pool manage karna aur tasks submit karna. Manually thread create karne se better.

Q10. ThreadLocal kya hai?

Har thread apna alag variable copy maintain karta hai. Sharing nahi hoti.