A daemon thread in Java is a low-priority thread that runs in the background to perform tasks such as garbage collection or provide services to user threads. The life of a daemon thread depends on the mercy of user threads, meaning that when all user threads finish their execution, the Java Virtual Machine (JVM) automatically terminates the daemon thread. Daemon threads serve user threads by handling background tasks and have no role other than supporting the main execution. Some examples of daemon threads in Java include garbage collection (gc) and finalizer.

To check if a thread is a daemon thread, we can call the isDaemon() method. To specify that a thread is a daemon thread, we can call the setDaemon() method with the argument true . It is important to note that the setDaemon() method can only be called before the thread has been started. Once the thread is running, we cannot modify its daemon status.

In summary, a daemon thread in Java is a low-priority thread that runs in the background to perform tasks such as garbage collection or provide services to user threads. Its life depends on the mercy of user threads, and it has no role other than supporting the main execution. We can check if a thread is a daemon thread using the isDaemon() method, and we can specify that a thread is a daemon thread using the setDaemon() method with the argument true.