Java setDaemon()方法
线程类的setDaemon()方法用于将线程标记为守护线程或用户线程。它的寿命取决于用户线程，即所有用户线程死亡时，JVM会自动终止该线程。必须在线程启动之前调用它。
如果在声明线程之后调用setDaemon()方法，则此方法将引发
IllegalThreadStateException 。
语法
public final void setDaemon(boolean on)
参数
开启: 如果为true，则将该线程标记为守护程序线程。
返回
如果线程是守护程序线程，则此方法将返回true，否则返回false。
异常
IllegalThreadStateException: 如果线程处于活动状态。
SecurityException: 如果当前线程无法修改该线程。
示例1
public class JavaSetDaemonExp1 extends Thread
{
public void run()
{
//checking for daemon thread
if(Thread.currentThread().isDaemon())
{
System.out.println("daemon thread work");
}
else
{
System.out.println("user thread work");
}
}
public static void main(String[] args)
{
// creating three threads
JavaSetDaemonExp1 t1=new JavaSetDaemonExp1();
JavaSetDaemonExp1 t2=new JavaSetDaemonExp1();
JavaSetDaemonExp1 t3=new JavaSetDaemonExp1();
// set user thread t1 to daemon thread
t1.setDaemon(true);
//call run() method
t1.start();
// set user thread t2 to daemon thread
t2.setDaemon(true);
// start of threads
t2.start();
t3.start();
}
}
输出:
daemon thread work
daemon thread work
user thread work
示例2
在线程启动后调用setDaemon()方法时。
public class JavaSetDaemonExp2 extends Thread
{
public void run()
{
System.out.println("Name of thread: "+Thread.currentThread().getName());
//
//checking for daemon thread
System.out.println("Daemon: "+Thread.currentThread().isDaemon());
}
public static void main(String[] args)
{
// creating two threads
JavaSetDaemonExp2 t1=new JavaSetDaemonExp2();
JavaSetDaemonExp2 t2=new JavaSetDaemonExp2();
// call run() method
t1.start();
// this will throw exception here
t1.setDaemon(true);
// call run() method
t2.start();
}
}
输出:
Name of thread: Thread-0
Daemon: false
Exception in thread "main" java.lang.IllegalThreadStateException
at java.lang.Thread.setDaemon(Thread.java:1359)
at JavaSetDaemonExp2.main(JavaSetDaemonExp2.java:17)
