what are the Threads runs when a java program running?

well when a program is running, there are threads that we create that are running. If your program is a simple console program, then there is a main thread which executed the main method and other threads that you create in the main thread. Also there are a few daemon threads run by the JVM. I know of one such thread i.e. the garbage collector but I'm sure there would many more like that...

I've put a code example called ThreadLister in the Code Barn. It enumerates all active threads. If you run that in a GUI app, or a web app, there will be quite a few more threads than if you run it from the command line.