JAVA用户线程&守护线程的区别

/**
* Marks this thread as either a daemon thread or a user thread. The
* Java Virtual Machine exits when the only threads running are all
* daemon threads.
* <p>
* This method must be called before the thread is started.
* <p>
* This method first calls the <code>checkAccess</code> method
* of this thread
* with no arguments. This may result in throwing a
* <code>SecurityException </code>(in the current thread).
*
* @param      on   if <code>true</code>, marks this thread as a
*                  daemon thread.
* @exception  IllegalThreadStateException  if this thread is active.
* @exception  SecurityException  if the current thread cannot modify
*               this thread.
* @see        #isDaemon()
* @see        #checkAccess
*/
public final void setDaemon(boolean on) {
checkAccess();
if (isAlive()) {
throw new IllegalThreadStateException();
}
daemon = on;
}

package daemon;

/**
* 当所有用户线程(也就普通线程)都已退出，只剩下守护线程时
* JVM会退出，守护线程也会被kill掉
*(主要还有一个普通线程在运行，JVM就不会退出)
*/
public class DeamonThreadTest {
public static void main(String[] args) {
//创建一个用户线程
Thread userThread=new Thread(){
public void run(){
for(int i=1;i<=5;i++){
try {
Thread.sleep(200);
System.out.println("用户线程第"+i+"次运行.....");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("用户线程退出.....");
}
};
//创建一个用户模拟守护线程的线程
Thread daemonThread=new Thread(){
public void run(){
for(int i=1;i<=99999;i++){
try {
Thread.sleep(50);
System.out.println("守护线程第"+i+"次运行.....");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("守护线程退出.....");
}
};
//让daemonThread成为守护线程
daemonThread.setDaemon(true);//这里必须在启动前设置，如果不设置，默认人是用户线程
userThread.start();
daemonThread.start();
}
}