固定线程池和缓存线程池之间的区别。

执行器框架是使用线程池概念设计的。线程池是重用已经创建的线程的方法，而不是每次执行当前任务都创建一个新线程的方法。

Executors类提供了一种工厂方法来创建线程池。ThreadPoolExecutor类是从许多Executors工厂方法返回的执行器的基本实现。

固定线程池示例

public class Main {
   public static void main(String args[]) throws InterruptedException {
      ExecutorService executors = Executors.newFixedThreadPool(4);
      CountDownLatch latch= new CountDownLatch(2);
      executors.submit(new Service1(latch));
      executors.submit(new Service2(latch));
      latch.await();
      System.out.println("Done");
   }

import java.util.concurrent.CountDownLatch;
public class Service1 implements Runnable {
   CountDownLatch latch;
   public Service1(CountDownLatch latch) {
      super();
      this.latch = latch;
   }
   @Override
   public void run() {
      try {
         Thread.sleep(20000);
      } catch (InterruptedException e) {
            //TODO自动生成的捕获块
            e.printStackTrace();
         }
         latch.countDown();
         System.out.println("Services2"+latch.getCount());
      }
   }
   import java.util.concurrent.CountDownLatch;
   public class Service2 implements Runnable {
      CountDownLatch latch;
      public Service2(CountDownLatch latch) {
         super();
         this.latch = latch;
      }
      @Override
      public void run() {
         try {
            Thread.sleep(20000);
         } catch (InterruptedException e) {
         //TODO自动生成的捕获块
         e.printStackTrace();
      }
   latch.countDown();
   System.out.println("Services2"+latch.getCount());
   }
}