Difference between the Thread class and the Runnable interface?


Extending the Thread Class:

When you extend the Thread class, your custom class becomes a subclass of Thread and inherits its behavior and methods.

Extending Thread allows you to override the run() method, where you define the code that will be executed in the thread.

Here are some considerations when using the Thread class:

a. Advantages:

Simplicity: Extending the Thread class can be simpler if you don't need to extend another class simultaneously or implement multiple interfaces.

Direct Access to Thread Methods: As a subclass of Thread, you have direct access to methods like start(), join(), sleep(), and interrupt(), which are useful for managing and controlling the thread's lifecycle.

b. Disadvantages:

Limited Inheritance: Java supports single inheritance, so by extending Thread, you can't extend any other class.

Reduced Flexibility: By directly extending Thread, your code is tightly coupled with the threading mechanism, which may limit code reuse and flexibility.

Here's an example of creating a thread by extending the Thread class:


public class MyThread extends Thread {
@Override 
public void run() { 
// Code to be executed in the thread 
 } 
}

To start the thread, you can create an instance of your custom MyThread class and call the start() method on it.


Implementing the Runnable Interface:

When you implement the Runnable interface, your custom class represents a task that can be executed by a thread.

Implementing Runnable requires you to define the run() method, where you specify the code to be executed in the thread.

Here are some considerations when using the Runnable interface:

a. Advantages:

Better Separation of Concerns: By implementing Runnable, you separate the task from the threading mechanism, promoting better code organization and separation of concerns.

Enhanced Code Reusability: Implementing Runnable allows you to reuse the same task implementation with different threading mechanisms, such as using a Thread object or submitting it to an ExecutorService.

b. Disadvantages:

Indirect Access to Thread Methods: Unlike extending Thread, implementing Runnable does not provide direct access to methods like start(), join(), or sleep(). 

However, you can access them through a Thread object if needed.

Here's an example of creating a thread by implementing the Runnable interface:


public class MyRunnable implements Runnable {
@Override

    public void run() {
// Code to be executed in the thread 
 }
}

To start the thread, you need to create an instance of your custom MyRunnable class and pass it to a Thread object's constructor.


Then, you can call the start() method on the Thread object to begin the execution of the thread.


MyRunnable myRunnable = new MyRunnable(); 
Thread thread = new Thread(myRunnable);
 thread.start();

By implementing Runnable, you achieve better separation of concerns, code reusability, and flexibility, as it allows you to extend other classes or implement multiple interfaces while defining the task to be executed in the thread.


In general, it is recommended to implement Runnable over extending Thread unless you specifically require direct access to the Thread class's methods or need to extend another class simultaneously.

 Implementing Runnable promotes better code organization, and separation of concerns, and enables better reuse of the task implementation.