Final answer:
The JVM terminates daemon threads when there are no user threads left because daemon threads exist to support user threads and their tasks. Once user threads finish, daemon threads are no longer needed, which signals the JVM to end the process, ensuring an orderly application termination and system resource release.
Step-by-step explanation:
The reason why the JVM (Java Virtual Machine) terminates daemon threads when there are no user threads remaining is directly related to the purpose of daemon threads within a Java application. Daemon threads are meant to serve user threads and are typically used to perform background tasks, such as garbage collection or housekeeping operations. In Java, user threads are considered the main workers of the application, and their completion determines when the application has finished its purpose.
When the last user thread terminates, the JVM assumes that the application has completed its execution, and therefore, there is no need for the daemon threads to continue running. As their sole purpose is to support the user threads, they are no longer necessary once the user threads have finished. This is why the JVM ends the process and with it, all remaining daemon threads.
This behavior is designed to prevent background tasks from keeping an application alive indefinitely after all user tasks have been completed. It ensures that the Java application terminates in an orderly fashion, releasing all system resources and allowing the operating system to reclaim memory and process space.