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 Thread and override run().
Implement Runnable interface and implement run() method.
Start a thread by calling start(), which internally calls run().
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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