Java----多线程以及线程池

1.多线程

for 循环采用串行方式，会消耗很长时间
多线程可以使 for 循环并行执行，节约时间

final CountDownLatch latch= new CountDownLatch(times);

times 为循环次数也是创建的线程数

        for (int i = 0; i < times; i++) {

            final int j = i;

            Thread thread = new Thread(new Runnable() {
                @Override
                public void run() 
                	{
                   			写入循环体
                        	latch.countDown();

                    } 
            });
            thread.start();

        }
        
        try {
            latch.await();    等待子线程结束
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }

2.线程池

 ExecutorService es = Executors.newFixedThreadPool(1000);
 指定线程池有1000个线程，根据需要指定
 
 for (String project : cloudEyeAlarmMap.keySet()) {
     es.execute(new Runnable() {
         @Override
         public void run() 
                          {
                           写入循环体 
                          }
     });
 }
 try {
        es.shutdown();
        es.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);
        一直等待子线程结束
     }
 catch (InterruptedException e) {
        e.printStackTrace();
 }