线程池

线程池是为了避免每次创建线程和销毁线程所带来的性能问题，原理和连接池差不多，在线程池的编程模型下，任务的提交是交给线程池的，而不是直接交给某个线程，线程池拿到某个任务后，它就在线程池内部查找有没有空余的线程，再把任务交给内部某个空余的线程，这就是封装，记住，任务是交给线程池，一个线程同时只能执行一个任务，但可以同时向线程池中提交多个任务。

package Thread02;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadPoolTest {
    public static void main(String[] args) {
        ExecutorService threadPool = Executors.newFixedThreadPool(3);//在线程池中放3个线程
        ExecutorService threadPool2 = Executors.newCachedThreadPool();//创建缓存线程池，可以自动增加新线程，线程的数目不定
        ExecutorService executor = Executors.newSingleThreadExecutor();//创建单一线程池，假如里面的线程死了，它会再创建一个线程
        for (int i = 1; i <= 10; i++) {
            final int task=i;
            threadPool.execute(new Runnable() {
                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    for (int j = 1; j <= 10; j++) {
                        try {
                            Thread.sleep(20);
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName()
                                + " is loop of " + j+" for task for "+task);
                    }
                }
            });
        }
        System.out.println("has commited!");
        threadPool.shutdown();//关闭线程池
    }
}

用线程池启动定时器

package Thread02;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class ThreadPoolTest {
    public static void main(String[] args) {            
        Executors.newScheduledThreadPool(3).schedule(new Runnable() {

            @Override
            public void run() {
                // TODO Auto-generated method stub
                System.out.println("欢迎光临！");
            }
        }, 2,TimeUnit.SECONDS );
    }
}