多线程4种实现

1，继承Thread类

2，实现Runnable接口（无返回值）

3，实现Callable接口（有返回值；依赖FutureTask类）

4，线程池（依赖ThreadPoolExecutor）

        五个实现类：

        Executors.newScheduledThreadPool(1);//了解
        Executors.newWorkStealingPool(1);//java8新特性

        ExecutorService threadPool = Executors.newFixedThreadPool(5);//一池5个处理线程
        ExecutorService threadPool = Executors.newFixedThreadPool(1);//一池1个线程
        ExecutorService threadPool = Executors.newCachedThreadPool();//一池N个线程

　　七大参数：

        ExecutorService threadPool = new ThreadPoolExecutor(2,
                5,
                1L,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(3),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.CallerRunsPolicy());//                                                                   

　　

拒绝策略：jdk内置的拒绝策略，AbortPolicy;CallerRunsPolicy;DiscardPolicy;DiscardPolicy,均实现RejectedExecutionHandler接口