如何在newFixedThreadPool环境中实现多线程

package com.hao.thread;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ThreadTest {

  public static void main(String[] args) {
    long start = System.currentTimeMillis();
    System.out.println(action());
    long end = System.currentTimeMillis();
    System.out.println(end - start);
  }

  public static List<String> action() {
    List<String> list = new ArrayList<String>();
    ExecutorService pool = Executors.newFixedThreadPool(3);
    Future<String> submit1 = pool.submit(() -> action1("action1"));
    Future<String> submit2 = pool.submit(() -> action2("action2"));
    Future<String> submit3 = pool.submit(() -> action3("action3"));
    try {
      list.add(submit1.get());
      list.add(submit2.get());
      list.add(submit3.get());
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      pool.shutdown();
    }
    return list;
  }

  private static String action1(String action1) {
    sleep(5000);
    return action1 + " # " + Thread.currentThread().getName();
  }

  private static String action2(String action2) {
    sleep(5000);
    return action2 + " # " + Thread.currentThread().getName();
  }

  private static String action3(String action3) {
    sleep(5000);
    return action3 + " # " + Thread.currentThread().getName();
  }

  private static void sleep(long millis) {
    try {
      Thread.sleep(millis);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}