Thread vs Runnable in Java: Key Differences and When to Use Each

In Java, Thread is a class that represents a thread of execution, while Runnable is a functional interface that defines a task to run in a thread. You can extend Thread to create a thread or implement Runnable to separate the task from the thread, allowing more flexible and reusable code.

Quick Comparison

Here is a quick side-by-side comparison of Thread and Runnable in Java.

Factor	Thread	Runnable
Type	Class	Interface
Inheritance	Must extend Thread class	Can be implemented by any class
Task vs Thread	Represents both thread and task	Represents only the task to run
Multiple Inheritance	Cannot extend another class (Java single inheritance)	Can implement along with extending another class
Reusability	Less reusable, tightly coupled with thread	More reusable, separates task from thread
Usage	Create thread by extending and overriding run()	Create task by implementing run() and passing to Thread

Key Differences

Thread is a concrete class in Java that represents a thread of execution. When you extend Thread, you create a new class that is itself a thread, and you override its run() method to define the code that runs in that thread.

Runnable is a functional interface with a single method run(). It represents a task or job that can be executed by a thread. You implement Runnable to separate the task from the thread itself, which allows your class to extend another class if needed.

Using Runnable promotes better design by decoupling the task from the thread management. It also allows multiple threads to share the same task object. Extending Thread is simpler but less flexible because Java does not support multiple inheritance, so you cannot extend any other class if you extend Thread.

Code Comparison

This example shows how to create a thread by extending the Thread class and overriding its run() method.

java

class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("Thread running by extending Thread class");
    }
}

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

Output

Thread running by extending Thread class

Runnable Equivalent

This example shows how to create a task by implementing the Runnable interface and passing it to a Thread object.

java

class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Thread running by implementing Runnable interface");
    }
}

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

Output

Thread running by implementing Runnable interface

When to Use Which

Choose Runnable when you want to separate the task from the thread, need to extend another class, or want to reuse the same task across multiple threads. It is the preferred approach for most multithreading tasks due to its flexibility.

Choose extending Thread when you want a quick and simple thread creation without needing to extend any other class or when you want to override other Thread methods directly. However, this approach is less flexible and less reusable.

Key Takeaways

Use Runnable to separate task logic from thread control for better flexibility.

Extending Thread limits your class from extending other classes due to Java's single inheritance.

Implementing Runnable allows sharing the same task across multiple threads.

Extending Thread is simpler but less reusable and flexible.

Prefer Runnable in most cases for clean, maintainable multithreaded code.