线程池ExecutorService 的使用

线程池的方法

    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the {@code Executor} implementation.
     *
     * @param command the runnable task 运行Runnale任务，定义一个类实现Runnale，或者直接使用lambda实现()->{}
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution
     * @throws NullPointerException if command is null
     */
      void execute(Runnable command);
/**
     * Submits a value-returning task for execution and returns a
     * Future representing the pending results of the task. The
     * Future's {@code get} method will return the task's result upon
     * successful completion.
     *
     * <p>
     * If you would like to immediately block waiting
     * for a task, you can use constructions of the form
     * {@code result = exec.submit(aCallable).get();}
     *
     * <p>Note: The {@link Executors} class includes a set of methods
     * that can convert some other common closure-like objects,
     * for example, {@link java.security.PrivilegedAction} to
     * {@link Callable} form so they can be submitted.
     *
     * @param task the task to submit 定义一个类实现
     * @param <T> the type of the task's result 可以指定返回值类型
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    <T> Future<T> submit(Callable<T> task);
 
    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's {@code get} method will
     * return the given result upon successful completion.
     *
     * @param task the task to submit 运行Runnale任务，定义一个类实现Runnale，或者直接使用lambda实现()->{}
     * @param result the result to return 指定类型返回
     * @param <T> the type of the result
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    <T> Future<T> submit(Runnable task, T result);

    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's {@code get} method will
     * return {@code null} upon <em>successful</em> completion.
     *
     * @param task the task to submit
     * @return a Future representing pending completion of the task 返回一个任意类型的返回值
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    Future<?> submit(Runnable task);

1. execute 无返回值

2. submit 有返回值

//创建 线程池
// 使用 Runnable 
  public class T03_Runnable {


ExecutorService executor = Executors.newFixedThreadPool(8);
 List<Future> futureList = new ArrayList<>();
                for (int b = 0;b<threadNum;b++){
                   
                    

                    Future<?> submit = executor.submit(() -> {
                        work()
                        
                    });
                    futureList.add(submit);
                }

                try {
                    for (Future future : futureList) {
                        System.out.println(future.get());//打印null
                    }
                } catch (InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                }

      //
      public void work(){
             System.out.println("start thread "+Thread.currentThread().getName()+" thredNum is "+thredNum);
      }

}
// 使用 callable
  public class T03_Callable {


    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Callable<String> callable  = new Callable<String>() {
            @Override
            public String call() throws Exception {
                return Thread.currentThread().getName()+" hello Callable";
            }
        };
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        Future<String> future = executorService.submit(callable);
      // 
      //  future.get() ：获取异步执行的结果，如果没有结果可用，此方法会阻塞直到异步计算完成
        String s = future.get();
        System.err.println(s);
        executorService.shutdown();
    }

}

参考：
https://blog.csdn.net/sx1119183530/article/details/79735348