Java.Multithreading.What is the difference between Thread and Runnable?

Let’s break it down step by step:

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🧠 Core Difference

Concept	Thread	Runnable
What is it?	A class that represents a thread of execution	A functional interface (task to run in a thread)
Role	Executes the code	Defines the code to run
Relationship	Thread is both a task and the runner	Runnable is just the task; needs a thread to run it
Flexibility	❌ Less flexible (extends Thread)	✅ More flexible (can be reused/shared)
Usage	Thread t = new MyThread(); t.start();	Thread t = new Thread(new MyRunnable()); t.start();

⚙️ Code Comparison

🔸 Using Thread (Extending the class)

class MyThread extends Thread {
    public void run() {
        System.out.println("Running in MyThread");
    }
}

public class Main {
    public static void main(String[] args) {
        Thread t = new MyThread();
        t.start();
    }
}

🟡 Limit: Since Java supports only single inheritance, you can’t extend any other class.

🔹 Using Runnable (Implementing the interface)

class MyRunnable implements Runnable {
    public void run() {
        System.out.println("Running in MyRunnable");
    }
}

public class Main {
    public static void main(String[] args) {
        Thread t = new Thread(new MyRunnable());
        t.start();
    }
}

🟢 Advantage:

• More flexible (you can still extend another class)
• Encouraged for clean design
• Works better with ExecutorService, thread pooling, and modern APIs

🔥 Bonus: With Lambdas (because Runnable is a functional interface)

Thread t = new Thread(() -> System.out.println("Running with lambda"));
t.start();

🧠 This is the modern, preferred way for short, simple tasks.

✅ Summary

Feature	Thread	Runnable
Type	Class	Interface
Inheritance	Requires extending	Can be implemented with other classes
Flexibility	Less	More
Used With Executors	❌ Awkward	✅ Perfect fit
Preferred in modern code	❌ Not really	✅ Yes