Question

I have a Swing interface, when I click on a button a thread is created at infinity (the genus while(true)…).

My question is: when I close the main process, will the created threads be closed automatically?

Answer 1

Depends on if the threads you’ve started are daemon threads or not, and how you close the main process.

Here’s the relevant documentation from the standard library:

When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named main of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:

• The exit method of class Runtime has been called and the security manager has permitted the exit operation to take place.

• All threads that are not daemon threads have died, either by returning from the call to the run method or by throwing an exception that propagates beyond the run method.

So, if you shut down the main process by System.exit or by using jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) then all threads will die when you shut down.

If you simply let the main thread (the thread running public static void main) drop off the edge of the main method, then the threads will continue to run.