1、setDeamon

设置线程为后台运行的函数

public class SetDaemon
{
	public static void main(String[] args) throws InterruptedException
	{
		Thread tt=new Thread(new ThreadTest());
		tt.setDaemon(true);						//设置程序为后台运行
		tt.start();
		Thread.sleep(3);
	}
}

class ThreadTest implements Runnable
{
	public void run()
	{
		while(true)
		{
			System.out.println(Thread.currentThread().getName()+" is running...");
		}

	}
}

可见当父线程后台运行的线程自动结束。

2、join

强制CPU执行某个线程

public class SetDaemon
{
	public static void main(String[] args) throws InterruptedException
	{
		Thread tt=new Thread(new ThreadTest());
		tt.start();

		for(int i=0;i<10;i++)
		{
			if(i==5)
			{
				tt.join();
			}
			System.out.println(Thread.currentThread().getName()+i+" is running...");
		}
	}
}

class ThreadTest implements Runnable
{
	public void run()
	{
		for(int i=0;i<5;i++)
		{
			System.out.println(Thread.currentThread().getName()+i+" is running...");
		}

	}
}

3、interrupt

中断线程

public class SetDaemon
{
	public static void main(String[] args) throws InterruptedException
	{
		Thread tt=new Thread(new ThreadTest());
		tt.start();
		Thread.sleep(2000);
		System.out.println("The subthread is interupted in the main thread.");
		tt.interrupt();
		tt.join();
		System.out.println("The main thread is over.");
	}
}

class ThreadTest implements Runnable
{
	public void run()
	{
		try
		{
			System.out.println("The subthread is sleeping...");
			Thread.sleep(200000);
		}
		catch(Exception e)
		{
			e.printStackTrace();
			System.out.println("The subthread is interupted.");
			return;
		}
		System.out.println("The subthread is over.");
	}
}

注意：这里的线程中断和通常所讲的硬件中断并不是同一个概念，硬件中断是...（这个就不要讲啦），这里的中断可以理解成线程的状态被设置成了中断状态（即挂起了一个小旗，告诉其它线程‘哥处于中断状态’，禁止某些操作），此时执行某些函数会触发异常，被中断的线程进入到异常处理代码段。

请仔细体会以下代码：

public class SetDaemon
{
	public static void main(String[] args) throws InterruptedException
	{
		Thread tt=new Thread(new ThreadTest());
		tt.start();
		Thread.sleep(5);
		System.out.println("The subthread is interupted in the main thread.");
		tt.interrupt();
		tt.join();
		System.out.println("The main thread is over.");
	}
}

class ThreadTest implements Runnable
{
	public void run()
	{
		try
		{
			while(true)
			{
				System.out.println(Thread.currentThread().getName()+" is running...");
				Thread.sleep(1);
			}
		}
		catch(Exception e)
		{
			e.printStackTrace();
			System.out.println("The subthread is interupted.");
			return;
		}
		//System.out.println("The subthread is over.");
	}
}

可以使用isInterupt()查看线程是否被中断。

java多线程控制函数setDaemon，join，interupt