得到 ExecutorService 当前活动的线程数

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;


/**
 * 测试得到线程池中的当前活动线程
 * @author keji
 * @2013-4-7
 */
public class TestPool {
public static void main(String[] args) {

ExecutorService exec = null;
try{

exec = Executors.newFixedThreadPool(10);

//想线程池中放入三个任务
exec.execute(new Task());
exec.execute(new Task());
exec.execute(new Task());
//延迟一下,因为三个任务放入需要时间
Thread.sleep(200);

//重点到了!!

//将exec转换为ThreadPoolExecutor,ThreadPoolExecutor有方法 getActiveCount()可以得到当前活动线程数
int threadCount = ((ThreadPoolExecutor)exec).getActiveCount();
System.out.println(threadCount);


Thread.sleep(4000);


threadCount = ((ThreadPoolExecutor)exec).getActiveCount();
System.out.println(threadCount);

exec.execute(new Task());
exec.execute(new Task());

Thread.sleep(200);

threadCount = ((ThreadPoolExecutor)exec).getActiveCount();
System.out.println(threadCount);



}catch(Exception e){
e.printStackTrace();
}finally{
if(exec!=null){
exec.shutdown();
}
}

}

}
class Task implements Runnable{
@Override
public void run() {
try{
Thread.sleep(3000);
}catch(Exception e){
e.printStackTrace();
}
}

}