What happens if we call run directly instead start() method?

When you call the run() method directly instead of the start() method in a threading context, the code within run() executes on the current thread rather than creating a new, separate thread. This means that no new thread is initiated, and the tasks run sequentially on the existing thread.

Understanding run() vs. start()

Calling start()

The start() method is responsible for creating a new thread of execution. When you invoke start(), the Java Virtual Machine (JVM) allocates a new thread and then calls the run() method within that new thread. This allows multiple threads to execute concurrently, enabling parallel processing and improved application performance.

Example:

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

public class Main {
    public static void main(String[] args) {
        MyThread t = new MyThread();
        t.start(); // Creates a new thread and executes run()
    }
}

Output:

Thread is running.

Calling run() Directly

On the other hand, if you call the run() method directly, it does not create a new thread. Instead, the run() method executes in the context of the current thread, behaving like a regular method call. This means that the tasks within run() run sequentially on the existing thread, without any concurrency benefits.

Example:

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

public class Main {
    public static void main(String[] args) {
        MyThread t = new MyThread();
        t.run(); // Executes run() on the main thread
    }
}

Output:

Thread is running.