What is inter-thread communication in Java
💡 Concept: Inter-thread communication
Inter-thread communication allows threads to cooperate by waiting and notifying each other for coordinated execution.
📘 Quick Intro
Threads use wait(), notify(), and notifyAll() methods on shared objects to communicate and avoid race conditions.
🧠 Analogy
Think of inter-thread communication like a conversation where one thread waits for a signal to proceed and another thread sends that signal.
🔧 Technical Explanation
wait()causes the current thread to wait until notified.notify()wakes up one waiting thread.notifyAll()wakes up all waiting threads.- These methods must be called from synchronized context.
- Used to coordinate threads sharing resources.
🎯 Use Cases
- ✅ Producer-consumer problem solution.
- ✅ Thread coordination in multi-threaded apps.
- ✅ Avoid busy waiting and CPU wastage.
💻 Inter-thread Communication Example
class Message {
private String msg;
public synchronized void send(String m) {
this.msg = m;
notify();
}
public synchronized void receive() {
try {
wait();
System.out.println("Received: " + msg);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}
❓ Interview Q&A
Q1: What is inter-thread communication?
A: Coordination between threads using wait, notify, notifyAll.
Q2: What does wait() do?
A: Makes the thread wait until notified.
Q3: What is the difference between notify() and notifyAll()?
A: notify() wakes one thread, notifyAll() wakes all.
Q4: Can wait(), notify() be called outside synchronized block?
A: No, causes IllegalMonitorStateException.
Q5: What is producer-consumer problem?
A: Threads producing and consuming shared resources.
Q6: How to avoid busy waiting?
A: Using wait/notify instead of loops.
Q7: What happens if notify() is called with no waiting threads?
A: No effect.
Q8: What exceptions can wait() throw?
A: InterruptedException.
Q9: Can notifyAll() cause performance issues?
A: Yes, waking all threads may cause overhead.
Q10: How to safely use wait/notify?
A: Always inside synchronized blocks.
📝 MCQs
Q1. What is inter-thread communication?
- Parallel execution
- Coordination between threads
- Race condition
- Deadlock
Q2. What does wait() do?
- Starts thread
- Makes thread wait until notified
- Stops thread
- Kills thread
Q3. Difference between notify() and notifyAll()?
- Both wake one
- notify() wakes one, notifyAll() all
- Both wake all
- No difference
Q4. Can wait() be called outside synchronized?
- Yes
- No
- Sometimes
- Only in Java 9+
Q5. What is producer-consumer problem?
- Single thread
- Threads producing and consuming
- Deadlock
- Race condition
Q6. How to avoid busy waiting?
- Using loops
- Using sleep()
- Using wait/notify
- Ignoring
Q7. What happens if notify() called with no waiting threads?
- Exception
- No effect
- Crash
- Deadlock
Q8. What exceptions can wait() throw?
- IOException
- InterruptedException
- RuntimeException
- Error
Q9. Can notifyAll() cause performance issues?
- No
- Yes
- Sometimes
- Never
Q10. How to safely use wait/notify?
- Outside synchronized
- Inside synchronized blocks
- Anywhere
- Only in static methods
💡 Bonus Insight
Inter-thread communication is essential for effective thread coordination and resource sharing in Java concurrency.
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