How to create a thread in Java
💡 Concept: Creating threads in Java
Java supports thread creation by extending the Thread class or implementing the Runnable interface.
📘 Quick Intro
Threads can be created by subclassing Thread and overriding run(), or by implementing Runnable and passing it to a Thread object.
🧠 Analogy
Think of threads like workers in a factory, each doing their own task either assigned directly or through a common interface.
🔧 Technical Explanation
- Subclass
Threadand overriderun(). - Implement
Runnableinterface and implementrun()method. - Start a thread by calling
start(), which internally callsrun(). - Runnable approach is preferred for better design flexibility.
- Threads share process memory but execute independently.
🎯 Use Cases
- ✅ Concurrent tasks in GUI apps.
- ✅ Background processing in server applications.
- ✅ Parallel execution to improve performance.
💻 Java Thread Creation Example
// Extending Thread class
class MyThread extends Thread {
public void run() {
System.out.println("Thread running");
}
}
// Implementing Runnable
class MyRunnable implements Runnable {
public void run() {
System.out.println("Runnable running");
}
}
public class Demo {
public static void main(String[] args) {
MyThread t1 = new MyThread();
t1.start();
Thread t2 = new Thread(new MyRunnable());
t2.start();
}
}
❓ Interview Q&A
Q1: What are two ways to create a thread in Java?
A: Extending Thread class or implementing Runnable interface.
Q2: Which approach is preferred?
A: Runnable interface for flexibility.
Q3: What method is called to start a thread?
A: start().
Q4: Can you call run() directly?
A: Yes, but it runs in the current thread.
Q5: Do threads share memory?
A: Yes, process memory is shared.
Q6: What is the main advantage of Runnable?
A: Allows extending other classes.
Q7: What happens if start() is called twice?
A: IllegalThreadStateException.
Q8: Can a thread be restarted?
A: No.
Q9: What is a daemon thread?
A: Background thread that terminates with JVM.
Q10: How to stop a thread safely?
A: Use flags or interrupts.
📝 MCQs
Q1. What are two ways to create a thread in Java?
- Extending Thread
- Implementing Runnable
- Both
- None
Q2. Which approach is preferred?
- Thread class
- Runnable interface
- Callable interface
- Executor
Q3. What method starts a thread?
- run()
- start()
- init()
- execute()
Q4. Can you call run() directly?
- No
- Yes but runs in current thread
- Yes and starts new thread
- Never
Q5. Do threads share memory?
- No
- Yes
- Sometimes
- Depends
Q6. Main advantage of Runnable?
- None
- Allows extending other classes
- Faster
- Simpler
Q7. What if start() called twice?
- No effect
- IllegalThreadStateException
- Crash
- Ignore
Q8. Can thread be restarted?
- Yes
- No
- Sometimes
- Only in Java 9+
Q9. What is daemon thread?
- User thread
- Daemon thread
- Main thread
- System thread
Q10. How to stop thread safely?
- stop()
- kill()
- Use flags or interrupts
- None
💡 Bonus Insight
Choosing between Thread and Runnable affects flexibility and design in multi-threaded Java applications.
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