To see the difference, imagine the following story about burgers:

### Concurrent Burgers { #concurrent-burgers }

You go with your crush to get fast food, you stand in line while the cashier takes the orders from the people in front of you. 😍

<img src="/img/async/concurrent-burgers/concurrent-burgers-01.png" class="illustration">

import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.lucene.search.TotalHits.Relation;
import org.codelibs.fess.entity.FacetInfo;

<img src="/img/async/concurrent-burgers/concurrent-burgers-05.png" class="illustration">

기다리며 대화하는 동안, 때때로 여러분은 카운터에 표시되는 번호를 확인해 여러분 차례인지 봅니다.

그러다 어느 순간 마침내 여러분 차례가 됩니다. 여러분은 카운터에 가서 햄버거를 받고, 테이블로 돌아옵니다.

<img src="/img/async/concurrent-burgers/concurrent-burgers-06.png" class="illustration">

여러분과 짝사랑 상대는 햄버거를 먹으며 좋은 시간을 보냅니다. ✨

<img src="/img/async/concurrent-burgers/concurrent-burgers-07.png" class="illustration">

 * views are modifiable.
 *
 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
 * read operations will work correctly if the last write <i>happens-before</i> any reads. To allow
 * concurrent update operations, wrap your multimap with a call to {@link
 * Multimaps#synchronizedSetMultimap}.
 *

 * implement {@link java.util.RandomAccess}.
 *
 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
 * read operations will work correctly. To allow concurrent update operations, wrap your multimap
 * with a call to {@link Multimaps#synchronizedListMultimap}.
 *
 * <p>See the Guava User Guide article on <a href=

 * views are modifiable.
 *
 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
 * read operations will work correctly if the last write <i>happens-before</i> any reads. To allow
 * concurrent update operations, wrap your multimap with a call to {@link
 * Multimaps#synchronizedSetMultimap}.
 *

import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;

import org.apache.logging.log4j.LogManager;

為了理解差異，請想像以下有關漢堡的故事：

### 並行漢堡 { #concurrent-burgers }

你和你的戀人去速食店，排隊等候時，收銀員正在幫排在你前面的人點餐。😍

<img src="/img/async/concurrent-burgers/concurrent-burgers-01.png" class="illustration">

輪到你了，你給你與你的戀人點了兩個豪華漢堡。🍔🍔

<img src="/img/async/concurrent-burgers/concurrent-burgers-02.png" class="illustration">

收銀員通知廚房準備你的漢堡（儘管他們還在為前面其他顧客準備食物）。

<img src="/img/async/concurrent-burgers/concurrent-burgers-03.png" class="illustration">

你付钱了。 💸

收银员给你轮到的号码。

<img src="/img/async/concurrent-burgers/concurrent-burgers-04.png" class="illustration">

当你在等待的时候，你和你的恋人一起去挑选一张桌子，然后你们坐下来聊了很长时间（因为汉堡很豪华，需要一些时间来准备）。

当你和你的恋人坐在桌子旁，等待汉堡的时候，你可以用这段时间来欣赏你的恋人是多么的棒、可爱和聪明✨😍✨。

<img src="/img/async/concurrent-burgers/concurrent-burgers-05.png" class="illustration">

 * implement {@link java.util.RandomAccess}.
 *
 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
 * read operations will work correctly. To allow concurrent update operations, wrap your multimap
 * with a call to {@link Multimaps#synchronizedListMultimap}.
 *
 * <p>See the Guava User Guide article on <a href=