JUC之线程池

package juc.day03;


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

public class ThreadPoolTest {
    public static void main(String[] args) {
        //Executor --->   ExecutorService
        //一个线程里创建8个工作线程
        ExecutorService service = Executors.newFixedThreadPool(2);
        try{
            for (int i = 1; i <= 4 ; i++) {
                service.execute(()->{
                    System.out.println("银行工作人员--"+Thread.currentThread().getName()+"--\t 提供服务");
                });
            }
        }finally {
            service.shutdown();
        }


    }
}

  ExecutorService service = Executors.newSingleThreadExecutor();//只有一个线程
  ExecutorService service1 = Executors.newCachedThreadPool();//N个线程，自动扩容

源码

 public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>()));
    }

这三个底层都是new ThreadPoolExecutor();
用到了阻塞队列
有七个参数

public ThreadPoolExecutor(int corePoolSize,//常驻线程数
                              int maximumPoolSize,//最大线程数
                              long keepAliveTime,//线程存活时间
                              TimeUnit unit,//存活时间单位
                              BlockingQueue<Runnable> workQueue,//候客区，等候区
                              ThreadFactory threadFactory,//线程创建工厂
                              RejectedExecutionHandler handler//拒绝策略,表示候客区满了后的策略) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

线程池底层工作原理（参考银行服务窗口，等候区）

这三个用哪一个，都不用，使用自定义的线程池

处理的任务数，为最大线程数+队列长度,如果超过这个长度，策略将会执行

拒绝策略
1.AbortPolicy ----> 报异常（中断策略）
2.CallerRunsPolicy----->将任务回退到调用者,不会抛异常 --------实际测试结果返回给了main线程
3.DiscardOldestPolicy------>等待时间最长的任务，直接抛弃
4.DiscardPolicy------->抛弃策略，超过了处理数，直接丢弃