Creating a thread without implementing Runnable interface in Java

Introduction

In Java, multithreading is an essential concept for building concurrent and parallel applications. Traditionally, to create a new thread, developers would implement the Runnable interface and override the run() method. However, there is an alternative way to create a thread without implementing the Runnable interface in Java.

In this article, we will explore how to create a thread without implementing the Runnable interface and discuss the advantages and disadvantages of this approach.

The Thread class

In addition to implementing the Runnable interface, Java provides another way to create a thread by extending the Thread class. The Thread class is a built-in class in Java that represents a thread of execution. By extending this class, we can directly create threads without having to implement the Runnable interface.

To create a thread by extending the Thread class, we need to follow these steps:

1. Create a new class that extends the Thread class.
2. Override the run() method, which is the entry point for the thread's execution.

Here's an example that demonstrates how to create a thread by extending the Thread class:

public class MyThread extends Thread {
    @Override
    public void run() {
        // The code to be executed in the new thread
        System.out.println("Running in a new thread");
    }
}

In the above example, we have created a new class MyThread that extends the Thread class. We have overridden the run() method to define the code that will be executed in the new thread.

To start the thread, we need to create an instance of the MyThread class and invoke its start() method:

public class Main {
    public static void main(String[] args) {
        MyThread thread = new MyThread();
        thread.start();
        
        // The code executing in the main thread
        System.out.println("Running in the main thread");
    }
}

When we invoke the start() method, it creates a new thread and invokes the run() method in the new thread concurrently with the main thread.

Advantages of extending the Thread class

Using the Thread class to create a thread has certain advantages:

1. Simplicity: Extending the Thread class allows you to define the code to be executed in the new thread directly within the class itself. This eliminates the need to separately implement the Runnable interface and provide an instance of it to the Thread constructor.

2. Object-oriented approach: By extending the Thread class, you can encapsulate the behavior of the thread within a class, making it easier to manage and maintain.

3. Inheritance: Extending the Thread class allows you to override other methods and add additional functionalities as needed.

Disadvantages of extending the Thread class

While extending the Thread class to create a thread has its advantages, it also has some disadvantages:

1. Limited inheritance: Java does not support multiple inheritance, so by extending the Thread class, you are prohibiting your class from inheriting any other class. This can be a limitation if your class needs to inherit from another class.

2. Lack of flexibility: The Thread class defines a fixed interface for creating and managing a thread. If you need more control over the thread's execution or want to implement a different concurrency mechanism, the Runnable interface provides more flexibility.

3. Performance impact: Each new thread created by extending the Thread class consumes system resources, such as memory. Creating a large number of threads can affect the overall performance of the application, especially in resource-constrained environments.

Conclusion

In Java, creating a thread without implementing the Runnable interface is possible by extending the Thread class. While this approach offers simplicity and an object-oriented approach, it also has limitations and may not be suitable for all scenarios.

When deciding whether to implement Runnable or extend Thread, consider the specific requirements of your application. If you need more flexibility, better code organization, and the ability to use multiple inheritance, implementing Runnable is a better choice. On the other hand, if simplicity and encapsulation are more important, extending the Thread class can be a viable option.

Understanding the pros and cons of both approaches will help you make an informed decision while designing concurrent and parallel applications in Java.