Main Thread in Java Cannot Be a Daemon Thread

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Question :

In Java Can we make the main() thread a daemon thread?

Réponse :

In Java, the main() thread cannot be made a daemon thread. The main() method is the entry point of any Java application, and the thread that executes it is the main thread. By design, the main thread is a user thread, and it cannot be converted to a daemon thread.

Daemon threads are designed to run in the background and provide services to user threads. They are terminated when all user threads finish executing. Since the main thread is a user thread, it will keep the JVM running until it completes its execution, regardless of the state of any daemon threads.

If you need to have a daemon thread running alongside your application, you can create a separate thread and set it as a daemon using the setDaemon(true) method before starting it. Here’s an example:

public class DaemonThreadExample {
    public static void main(String[] args) {
        // Create a daemon thread
        Thread daemonThread = new Thread(() -> {
            while (true) {
                System.out.println("Daemon thread is running...");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
        });

        // Set the thread as a daemon
        daemonThread.setDaemon(true);
        daemonThread.start();

        // Main thread work
        System.out.println("Main thread is doing some work...");
        try {
            Thread.sleep(5000); // Simulate some work in the main thread
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }

        System.out.println("Main thread is done.");
        // The JVM will exit here, and the daemon thread will be terminated.
    }
}

In this example, the daemonThread is created and set as a daemon. The main thread does some work and then finishes, which will cause the JVM to exit, terminating the daemon thread.

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