守护线程类似于助手线程。非daemon线程就像前面的表演者。助手帮助表演者完成一项工作。工作完成后，执行者不再需要帮助来执行。由于不需要帮助，助手们离开了这个地方。因此，当非守护线程的任务结束时，守护线程就会离开。

守护线程和用户线程。通常程序员创建的所有线程都是用户线程(除非你指定它为守护线程或者你的父线程是守护线程)。用户线程通常用于运行我们的程序代码。除非所有用户线程都终止，否则JVM不会终止。

我想澄清一个误解:

Assume that if daemon thread (say B) is created within user thread (say A); then ending of this user thread/parent thread (A) will not end the daemon thread/child thread (B) it has created; provided user thread is the only one currently running. So there is no parent-child relationship on thread ending. All daemon threads (irrespective of where it is created) will end once there is no single live user thread and that causes JVM to terminate. Even this is true for both (parent/child) are daemon threads. If a child thread created from a daemon thread then that is also a daemon thread. This won't need any explicit daemon thread flag setting. Similarly if a child thread created from a user thread then that is also a user thread, if you want to change it, then explicit daemon flag setting is needed before start of that child thread.

守护进程： d（isk） a（nd） e（xecution） mon（itor） or or from de（vice） mon（itor）

Daemon(计算)的定义:

处理打印假脱机和文件传输等服务请求的后台进程，在不需要时处于休眠状态。

——来源:牛津词典英文版

Java中的守护线程是什么?

Daemon threads can shut down any time in between their flow, Non-Daemon i.e. user thread executes completely. Daemon threads are threads that run intermittently in the background as long as other non-daemon threads are running. When all of the non-daemon threads complete, daemon threads terminates automatically. Daemon threads are service providers for user threads running in the same process. The JVM does not care about daemon threads to complete when in Running state, not even finally block also let execute. JVM do give preference to non-daemon threads that is created by us. Daemon threads acts as services in Windows. The JVM stops the daemon threads when all user threads (in contrast to the daemon threads) are terminated. Hence daemon threads can be used to implement, for example, a monitoring functionality as the thread is stopped by the JVM as soon as all user threads have stopped.

守护线程就像一个普通的线程，除了JVM只会在其他非守护线程不存在时关闭。守护进程线程通常用于为应用程序执行服务。

守护进程线程通常被称为“服务提供者”线程。这些线程不应该用来执行程序代码，而应该用来执行系统代码。这些线程与您的代码并行运行，但JVM可以随时终止它们。当JVM没有发现用户线程时，它将停止用户线程，所有守护进程线程立即终止。我们可以使用以下方法将非守护线程设置为守护线程:

setDaemon(true)