Java background process and thread priority

1. Background thread: The task is running in the background and serves other threads. It is also called "daemon thread" or "Genie thread ". JVM garbage collection is a typical background thread. Features: If all foreground threads die, background threads automatically die. Set background Thread: the Thread object setDaemon (true); setDaemon (true) must be before start. Otherwise, an exception occurs in IllegalThreadStateException. The Thread created by the foreground Thread is the foreground Thread by default. Determine whether the Thread is a background Thread: Use the isDaemon () method of the Thread object; the new thread is the background thread only when the creation thread is a background thread. Example: class Daemon implements Runnable {public void run () {for (int I = 0; I <200; I ++) {System. out. println ("Daemon -->" + I) ;}} public class DaemonDemo {public static void main (String [] args) {/* Thread cThread = Thread. currentThread (); System. out. println (cThread. isAlive (); // cThread. setDaemon (true); System. out. println (cThread. isDaemon (); */Thread t = new Thread (new Daemon (); System. out. println (T. isDaemon (); for (int I = 0; I <10; I ++) {System. out. println ("main --" + I); if (I = 5) {t. setDaemon (true); t. start () ;}}} 2. thread priority: Each thread has a priority. The priority is only related to the number of times the thread gets the execution opportunity. The higher the thread priority, it must be executed first. The first running of a thread depends on the CPU scheduling. By default, the main thread has a normal priority, and the thread it creates has a normal priority. SetPriority (int x) and getPriority () of the Thread object to set and obtain the priority. MAX_PRIORITY: The value is 10MIN_PRIORITY: The value is 1NORM_PRIORITY: The value is 5 (the default priority of the main method). Note: The default priority of each thread is the same as that of the parent thread created, by default, the main thread has a normal Priority. The subthread created by the main thread also has a normal Priority. Example: class Priority implements Runnable {public void run () {for (int I = 0; I <200; I ++) {System. out. println ("Priority --" + I) ;}} public class PriorityDemo {public static void main (String [] args) {/*** the Thread priority is between [1, 10] */Thread. currentThread (). setPriority (3); System. out. println ("main =" + Thread. currentThread (). getPriority ();/** public final static int MIN_PRIORITY = 1; * public final static int NORM_PRIORITY = 5; * public final static int MAX_PRIORITY = 10; **/System. out. println (Thread. MAX_PRIORITY ); // ================================================ ========= Thread t = new Thread (new Priority ()); for (int I = 0; I <200; I ++) {System. out. println ("main" + I); if (I = 50) {t. start (); t. setPriority (10);} System. out. println ("-------------------------" + t. getPriority ());}}}