Types of Threads in Java

Multithreading is a crucial aspect of modern software development, allowing programs to execute multiple tasks simultaneously. Threads are the smallest units of execution within a process and provide a way to achieve concurrency. Java, with its robust multithreading support, offers developers a powerful framework to create, manage, and coordinate threads.

Benefits of Multithreading

Improved Performance: Multithreading enables the execution of multiple tasks concurrently, utilizing the available CPU cores efficiently and enhancing overall performance.
Responsiveness: Multithreading ensures that applications remain responsive to user interactions even when performing time-consuming operations.
Parallelism: Threads can be used to divide a complex task into smaller subtasks that can be executed in parallel, taking full advantage of multi-core processors.
Background Processing: Threads allow background processing of tasks, such as file I/O, network communication, or data processing, without blocking the main application flow.
Utilization of Resources: By utilizing multiple threads, programs can make better use of system resources, leading to better resource allocation and management.

Types of Threads

1. User Threads

User threads, also known as application threads, are threads that are explicitly created by the programmer to perform specific tasks. They play a direct role in the main functionality of the application. User threads continue executing until their task is completed or until the application explicitly terminates them.

In the earlier example, the UserThreadExample demonstrated the creation and execution of a user thread. These threads are vital for the core functionality of the program.

UserThreadExample.java

public class UserThreadExample {
    public static void main(String[] args) {
        Thread userThread = new Thread(() -> {
            for (int i = 1; i <= 5; i++) {
                System.out.println("User Thread - Count: " + i);
                try {
                    Thread.sleep(1000); 
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        userThread.start();
        // Main thread continues executing
        for (int i = 1; i <= 3; i++) {
            System.out.println("Main Thread - Count: " + i);
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

Output:

User Thread - Count: 1
Main Thread - Count: 1
Main Thread - Count: 2
User Thread - Count: 2
Main Thread - Count: 3
User Thread - Count: 3
User Thread - Count: 4
User Thread - Count: 5

Explanation

In this example, a user thread is created using a lambda expression. The thread counts from 1 to 5 while the main thread counts from 1 to 3. The two threads run concurrently, showcasing multithreading.

Daemon Threads

Daemon threads are threads that provide support to user threads. They run in the background and are considered "service" threads. Unlike user threads, daemon threads do not prevent the JVM from exiting, even if they are still running. When all user threads have finished executing, the JVM terminates, abruptly stopping any remaining daemon threads.

Daemon threads are commonly used for tasks such as automatic memory management (garbage collection) or other housekeeping activities that should not delay the program's termination.

DaemonThreadExample.java

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

        // Main thread continues executing
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Main thread exiting");
    }
}

Output:

Daemon Thread is running
Daemon Thread is running
Daemon Thread is running
Daemon Thread is running
Daemon Thread is running
Main thread exiting

Explanation

In this example, a daemon thread is created to run indefinitely, printing a message at regular intervals. The main thread sleeps for 5 seconds before printing an exit message. Notice how the daemon thread abruptly terminates when the main thread exits.

Conclusion

Multithreading is a foundational concept in Java that empowers developers to design responsive, efficient, and parallelizable applications. Understanding the distinctions between user threads and daemon threads, as well as their practical use cases, is pivotal for writing robust and high-performance code. With proper thread synchronization, developers can harness the benefits of concurrency while avoiding pitfalls associated with data corruption and race conditions. By mastering the art of multithreading, Java developers can unlock the full potential of modern computing systems.

Next TopicWhat is thread safety in Java? How do you achieve it?

← prev next →