Java Interview Question: Create and Run a Thread Using Runnable (With Example & Explanation)

 🔹 Introduction

Multithreading is a very important topic in Java interviews, especially for backend roles.

👉 One of the most commonly asked questions is:
How to create and run a thread using Runnable?

In this article, we will understand it step by step with examples.

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🔹 Problem Statement

Create a thread in Java using the Runnable interface and execute it.

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🔹 What is Runnable?

Runnable is a functional interface in Java that contains only one method:

public interface Runnable {
    void run();
}

👉 It is used to define a task that can be executed by a thread.

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🔹 Approach

1. Create a class that implements Runnable
2. Override the run() method
3. Pass object to Thread
4. Call start()

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🔹 Java Code (Runnable Implementation)

class MyTask implements Runnable {
    public void run() {
        System.out.println("Thread is running...");
    }
}

public class Main {
    public static void main(String[] args) {
        MyTask task = new MyTask();

        Thread thread = new Thread(task);
        thread.start();
    }
}

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🔹 Output

Thread is running...

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🔹 Using Lambda (Modern Approach)

Since Runnable is a functional interface, we can use lambda expressions.

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👨‍💻 Java Code (Lambda)

public class Main {
    public static void main(String[] args) {

        Runnable task = () -> {
            System.out.println("Thread running using lambda...");
        };

        Thread thread = new Thread(task);
        thread.start();
    }
}

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🔍 Important Interview Point

👉 Difference between start() and run():

• start() → creates new thread
• run() → runs in same thread

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🔹 Time Complexity

• Depends on task (not fixed)

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🔹 Key Takeaways

✔ Runnable is preferred over extending Thread
✔ Supports multiple inheritance
✔ Lambda makes code concise
✔ Very common interview question

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🔹 Conclusion

Understanding threads and Runnable is essential for backend and concurrent programming.

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