java常用类介绍及源码阅读（LinkedList）

Dear 丶 2022-01-23 10:13 199阅读 0赞

## java.util 类 LinkedList<E> ##

java.lang.Object
 java.util.AbstractCollection<E>
 java.util.AbstractList<E>
 java.util.AbstractSequentialList<E>
 java.util.LinkedList<E>

List 接口的链接列表实现。实现所有可选的列表操作，并且允许所有元素（包括 null）。

除了实现 List 接口外，LinkedList 类还为在列表的开头及结尾 get、remove 和 insert 元素提供了统一的命名方法。这些操作允许将链接列表用作堆栈、[队列][Link 1]或[双端队列][Link 2]。

此类实现 Deque 接口，为 add、poll 提供先进先出队列操作，以及其他堆栈和双端队列操作。

所有操作都是按照双重链接列表的需要执行的。在列表中编索引的操作将从开头或结尾遍历列表（从靠近指定索引的一端）。

操作效率：大部分效率都是o(n)的

同步：

**注意，此实现不是同步的。**如果多个线程同时访问一个链接列表，而其中至少一个线程从结构上修改了该列表，则它*必须* 保持外部同步。（结构修改指添加或删除一个或多个元素的任何操作；仅设置元素的值不是结构修改。）这一般通过对自然封装该列表的对象进行同步操作来完成。如果不存在这样的对象，则应该使用 [`Collections.synchronizedList`][Collections.synchronizedList] 方法来“包装”该列表。最好在创建时完成这一操作，以防止对列表进行意外的不同步访问，如下所示：

List list = Collections.synchronizedList(new LinkedList(...));

iterator ：

此类的 iterator 和 listIterator 方法返回的迭代器是*快速失败* 的：在迭代器创建之后，如果从结构上对列表进行修改，除非通过迭代器自身的 remove 或 add 方法，其他任何时间任何方式的修改，迭代器都将抛出 [`ConcurrentModificationException`][ConcurrentModificationException]。因此，面对并发的修改，迭代器很快就会完全失败，而不冒将来不确定的时间任意发生不确定行为的风险。

注意，迭代器的快速失败行为不能得到保证，一般来说，存在不同步的并发修改时，不可能作出任何硬性保证。快速失败迭代器尽最大努力抛出 ConcurrentModificationException。因此，编写依赖于此异常的程序的方式是错误的，正确做法是：*迭代器的快速失败行为应该仅用于检测程序错误。*

<table> 
 <tbody> 
 <tr> 
 <th colspan="2">构造方法摘要</th> 
 </tr> 
 <tr> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#LinkedList%28%29" rel="nofollow">LinkedList</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;构造一个空列表。</td> 
 </tr> 
 <tr> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#LinkedList%28java.util.Collection%29" rel="nofollow">LinkedList</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Collection.html" rel="nofollow">Collection</a>&lt;? extends&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&gt;&nbsp;c)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;构造一个包含指定 collection 中的元素的列表，这些元素按其 collection 的迭代器返回的顺序排列。</td> 
 </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
 <tr> 
 <th colspan="2">方法摘要</th> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#add%28E%29" rel="nofollow">add</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将指定元素添加到此列表的结尾。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#add%28int,%20E%29" rel="nofollow">add</a>(int&nbsp;index,&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;element)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在此列表中指定的位置插入指定的元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#addAll%28java.util.Collection%29" rel="nofollow">addAll</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Collection.html" rel="nofollow">Collection</a>&lt;? extends&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&gt;&nbsp;c)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;添加指定 collection 中的所有元素到此列表的结尾，顺序是指定 collection 的迭代器返回这些元素的顺序。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#addAll%28int,%20java.util.Collection%29" rel="nofollow">addAll</a>(int&nbsp;index,&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Collection.html" rel="nofollow">Collection</a>&lt;? extends&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&gt;&nbsp;c)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将指定 collection 中的所有元素从指定位置开始插入此列表。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#addFirst%28E%29" rel="nofollow">addFirst</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将指定元素插入此列表的开头。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#addLast%28E%29" rel="nofollow">addLast</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将指定元素添加到此列表的结尾。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#clear%28%29" rel="nofollow">clear</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;从此列表中移除所有元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#clone%28%29" rel="nofollow">clone</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此&nbsp;LinkedList&nbsp;的浅表副本。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#contains%28java.lang.Object%29" rel="nofollow">contains</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>&nbsp;o)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;如果此列表包含指定元素，则返回&nbsp;true。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Iterator.html" rel="nofollow">Iterator</a>&lt;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&gt;</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#descendingIterator%28%29" rel="nofollow">descendingIterator</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回以逆向顺序在此双端队列的元素上进行迭代的迭代器。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#element%28%29" rel="nofollow">element</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取但不移除此列表的头（第一个元素）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#get%28int%29" rel="nofollow">get</a>(int&nbsp;index)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表中指定位置处的元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#getFirst%28%29" rel="nofollow">getFirst</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表的第一个元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#getLast%28%29" rel="nofollow">getLast</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表的最后一个元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;int</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#indexOf%28java.lang.Object%29" rel="nofollow">indexOf</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>&nbsp;o)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表中首次出现的指定元素的索引，如果此列表中不包含该元素，则返回 -1。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;int</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#lastIndexOf%28java.lang.Object%29" rel="nofollow">lastIndexOf</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>&nbsp;o)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表中最后出现的指定元素的索引，如果此列表中不包含该元素，则返回 -1。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/ListIterator.html" rel="nofollow">ListIterator</a>&lt;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&gt;</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#listIterator%28int%29" rel="nofollow">listIterator</a>(int&nbsp;index)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表中的元素的列表迭代器（按适当顺序），从列表中指定位置开始。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#offer%28E%29" rel="nofollow">offer</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将指定元素添加到此列表的末尾（最后一个元素）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#offerFirst%28E%29" rel="nofollow">offerFirst</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在此列表的开头插入指定的元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#offerLast%28E%29" rel="nofollow">offerLast</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在此列表末尾插入指定的元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#peek%28%29" rel="nofollow">peek</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取但不移除此列表的头（第一个元素）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#peekFirst%28%29" rel="nofollow">peekFirst</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取但不移除此列表的第一个元素；如果此列表为空，则返回&nbsp;null。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#peekLast%28%29" rel="nofollow">peekLast</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取但不移除此列表的最后一个元素；如果此列表为空，则返回&nbsp;null。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#poll%28%29" rel="nofollow">poll</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取并移除此列表的头（第一个元素）</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#pollFirst%28%29" rel="nofollow">pollFirst</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取并移除此列表的第一个元素；如果此列表为空，则返回&nbsp;null。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#pollLast%28%29" rel="nofollow">pollLast</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取并移除此列表的最后一个元素；如果此列表为空，则返回&nbsp;null。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#pop%28%29" rel="nofollow">pop</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;从此列表所表示的堆栈处弹出一个元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#push%28E%29" rel="nofollow">push</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;e)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将元素推入此列表所表示的堆栈。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#remove%28%29" rel="nofollow">remove</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;获取并移除此列表的头（第一个元素）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#remove%28int%29" rel="nofollow">remove</a>(int&nbsp;index)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;移除此列表中指定位置处的元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#remove%28java.lang.Object%29" rel="nofollow">remove</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>&nbsp;o)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;从此列表中移除首次出现的指定元素（如果存在）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#removeFirst%28%29" rel="nofollow">removeFirst</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;移除并返回此列表的第一个元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#removeFirstOccurrence%28java.lang.Object%29" rel="nofollow">removeFirstOccurrence</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>&nbsp;o)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;从此列表中移除第一次出现的指定元素（从头部到尾部遍历列表时）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#removeLast%28%29" rel="nofollow">removeLast</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;移除并返回此列表的最后一个元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;boolean</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#removeLastOccurrence%28java.lang.Object%29" rel="nofollow">removeLastOccurrence</a>(<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>&nbsp;o)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;从此列表中移除最后一次出现的指定元素（从头部到尾部遍历列表时）。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a></code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#set%28int,%20E%29" rel="nofollow">set</a>(int&nbsp;index,&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html" rel="nofollow">E</a>&nbsp;element)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;将此列表中指定位置的元素替换为指定的元素。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;int</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#size%28%29" rel="nofollow">size</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回此列表的元素数。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"><code>&nbsp;<a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html" rel="nofollow">Object</a>[]</code></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#toArray%28%29" rel="nofollow">toArray</a>()</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回以适当顺序（从第一个元素到最后一个元素）包含此列表中所有元素的数组。</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;"> 
 <table> 
 <tbody> 
 <tr> 
 <td><code><code>&lt;T&gt; T[]</code></code></td> 
 </tr> 
 </tbody> 
 </table></td> 
 <td><code><a href="http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/LinkedList.html#toArray%28T%5B%5D%29" rel="nofollow">toArray</a>(T[]&nbsp;a)</code>&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回以适当顺序（从第一个元素到最后一个元素）包含此列表中所有元素的数组；返回数组的运行时类型为指定数组的类型。</td> 
 </tr> 
 </tbody> 
</table>

package java.util;
 import java.util.function.Consumer;
 public class LinkedList<E>
 extends AbstractSequentialList<E>
 implements List<E>, Deque<E>, Cloneable, java.io.Serializable {
 /**
 	 * 元素数量
 	 */
 transient int size = 0;
 
 /**
 	 * 首结点引用
 	 */
 transient Node<E> first;
 
 /**
 	 * 尾节点引用
 	 */
 transient Node<E> last;
 
 /**
 	 * 无参构造方法
 	 */
 public LinkedList() {
 }
 
 /**
 	 * 通过一个集合初始化，元素顺序有这个集合的迭代器返回顺序决定
 	 * 
 	 * @param c
 	 * 其元素将被放入此列表中的集合
 	 * @throws NullPointerException
 	 * 如果指定的集合是空的
 	 */
 public LinkedList(Collection<? extends E> c) {
 // 调用无参构造
 this();
 // 添加所有的元素
 addAll(c);
 }
 
 /**
 	 * 头插，内部使用
 	 */
 private void linkFirst(E e) {
 // 当前首结点
 final Node<E> f = first;
 // 构建新节点
 final Node<E> newNode = new Node<>(null, e, f);
 // 将newNode作为首节点
 first = newNode;
 // 如果原首节点为null，即原链表为null，则链表尾节点也设置为newNode
 if (f == null)
 last = newNode;
 else // 否则，原首节点的prev设置为newNode
 f.prev = newNode;
 size++; // 长度+1
 modCount++; // 修改次数+1
 }
 
 /**
 	 * 尾插
 	 */
 void linkLast(E e) {
 // 获取尾结点
 final Node<E> l = last;
 // 构建新节点
 final Node<E> newNode = new Node<>(l, e, null);
 // newNode作为尾节点
 last = newNode;
 // 如果原尾节点为null，即原链表为null，则链表首节点也设置为newNode
 if (l == null)
 first = newNode;
 else // 否则，原尾节点的next设置为newNode
 l.next = newNode;
 size++;
 modCount++;
 }
 
 /**
 	 * 在非空节点succ前插入节点值e
 	 */
 void linkBefore(E e, Node<E> succ) {
 final Node<E> pred = succ.prev;
 // 构建新节点
 final Node<E> newNode = new Node<>(pred, e, succ);
 // 设置newNode为succ的前节点
 succ.prev = newNode;
 // 如果succ.prev为null，即succ为首节点，则将newNode设置为首节点
 if (pred == null)
 first = newNode;
 else // 如果succ不是首节点
 pred.next = newNode;
 size++;
 modCount++;
 }
 
 /**
 	 * 删除首结点，返回存储的元素，内部使用
 	 */
 private E unlinkFirst(Node<E> f) {
 // 获取首结点存储的元素
 final E element = f.item;
 // 获取首结点的后继结点
 final Node<E> next = f.next;
 // 删除首结点
 f.item = null;
 f.next = null; // 便于垃圾回收
 // 首结点后继结点设为首结点
 first = next;
 // 如果原来首结点的后继结点为空，则尾结点设为null
 // 否则，原来首结点的后继结点的前驱结点设为null
 if (next == null)
 last = null;
 else
 next.prev = null;
 size--;
 modCount++;
 // 返回原来首结点存储的元素
 return element;
 }
 
 /**
 	 * 删除尾结点，返回存储的元素，内部使用
 	 */
 private E unlinkLast(Node<E> l) {
 // 获取尾结点存储的元素
 final E element = l.item;
 // 获取尾结点的前驱结点
 final Node<E> prev = l.prev;
 // 删除尾结点
 l.item = null;
 l.prev = null; // help GC
 // 原来尾结点的前驱结点设为尾结点
 last = prev;
 // 如果原来尾结点的前驱结点为空，则首结点设为null
 // 否则，原来尾结点的前驱结点的后继结点设为null
 if (prev == null)
 first = null;
 else
 prev.next = null;
 size--;
 modCount++;
 // 返回原来尾结点存储的元素
 return element;
 }
 
 /**
 	 * 删除指定非空结点，返回存储的元素
 	 */
 E unlink(Node<E> x) {
 // 获取指定非空结点存储的元素
 final E element = x.item;
 // 获取指定非空结点的后继结点
 final Node<E> next = x.next;
 // 获取指定非空结点的前驱结点
 final Node<E> prev = x.prev;
 /**
 		 * 如果指定非空结点的前驱结点为空，则指定非空结点的后继结点设为首结点 
 		 * 否则，指定非空结点的后继结点设为指定非空结点的前驱结点的后继结点，
 		 * 指定非空结点的前驱结点设为null
 		 */
 if (prev == null) {
 first = next;
 } else {
 prev.next = next;
 x.prev = null;
 }
 
 /**
 		 * 如果指定非空结点的后继结点为空，则指定非空结点的前驱结点设为尾结点 
 		 * 否则，指定非空结点的前驱结点设为指定非空结点的后继结点的前驱结点，
 		 * 指定非空结点的后继结点设为null
 		 */
 if (next == null) {
 last = prev;
 } else {
 next.prev = prev;
 x.next = null;
 }
 
 // 指定非空结点存储的元素设为null
 x.item = null;
 size--;
 modCount++;
 // 返回指定非空结点存储的元素
 return element;
 }
 
 /**
 	 * 获取首结点存储的元素
 	 * 
 	 * @return 首结点存储的元素
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 */
 public E getFirst() {
 // 获取首结点引用
 final Node<E> f = first;
 // 如果首结点为空，则抛出无该元素异常
 if (f == null)
 throw new NoSuchElementException();
 // 返回首结点存储的元素
 return f.item;
 }
 
 /**
 	 * 获取尾结点存储的元素
 	 * 
 	 * @return 尾结点存储的元素
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 */
 public E getLast() {
 // 获取尾结点引用
 final Node<E> l = last;
 // 如果尾结点为空，则抛出无该元素异常
 if (l == null)
 throw new NoSuchElementException();
 // 返回尾结点存储的元素
 return l.item;
 }
 
 /**
 	 * 删除首结点，返回存储的元素
 	 * 
 	 * @return 首结点存储的元素
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 */
 public E removeFirst() {
 // 获取首结点引用
 final Node<E> f = first;
 // 如果首结点为空，则抛出无该元素异常
 if (f == null)
 throw new NoSuchElementException();
 // 删除首结点，返回存储的元素
 return unlinkFirst(f);
 }
 
 /**
 	 * 删除尾结点，返回存储的元素
 	 * 
 	 * @return 尾结点存储的元素
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 */
 public E removeLast() {
 // 获取尾结点引用
 final Node<E> l = last;
 // 如果尾结点为空，则抛出无该元素异常
 if (l == null)
 throw new NoSuchElementException();
 // 删除尾结点，返回存储的元素
 return unlinkLast(l);
 }
 
 /**
 	 * 头部插入指定元素
 	 * 
 	 * @param e
 	 * 要添加的元素
 	 */
 public void addFirst(E e) {
 // 通过头插法来插入指定元素
 linkFirst(e);
 }
 
 /**
 	 * 尾部插入指定元素，该方法等价于add()
 	 * 
 	 * @param e
 	 * the element to add
 	 */
 public void addLast(E e) {
 linkLast(e);
 }
 
 /**
 	 * 判断是否包含指定元素
 	 * 
 	 * @param o
 	 * 判断链表是否包含的元素
 	 * @return {@code true} 如果链表包含指定的元素
 	 */
 public boolean contains(Object o) {
 // 返回指定元素的索引位置，不存在就返回-1，然后比较返回bool值
 return indexOf(o) != -1;
 }
 
 /**
 	 * 获取元素数量
 	 * 
 	 * @return 元素数量
 	 */
 public int size() {
 return size;
 }
 
 /**
 	 * 插入指定元素，返回操作结果,默认添加到末尾作为最后一个元素
 	 * 
 	 * @param e
 	 * 要添加到此链表中的元素
 	 * @return {@code true} (as specified by {@link Collection#add})
 	 */
 public boolean add(E e) {
 // 通过尾插法来插入指定元素
 linkLast(e);
 return true;
 }
 
 /**
 	 * 删除指定元素，默认从first节点开始，删除第一次出现的那个元素
 	 * 
 	 * @param o
 	 * 要从该列表中删除的元素（如果存在）
 	 * @return {@code true} 如果这个列表包含指定的元素
 	 */
 public boolean remove(Object o) {
 // 会根据是否为null分开处理。若值不是null，会用到对象的equals()方法
 if (o == null) {
 // 遍历链表，查找到指定元素后删除该结点，返回true
 for (Node<E> x = first; x != null; x = x.next) {
 if (x.item == null) {
 unlink(x);
 return true;
 }
 }
 } else {
 for (Node<E> x = first; x != null; x = x.next) {
 if (o.equals(x.item)) {
 unlink(x);
 return true;
 }
 }
 }
 // 查找失败
 return false;
 }
 
 /**
 	 * 将集合插入到链表尾部
 	 * 
 	 * @param c
 	 * 包含要添加到此链表中的元素的集合
 	 * @return {@code true} 如果该链表因添加而改变
 	 * @throws NullPointerException
 	 * 如果指定的集合是空的
 	 */
 public boolean addAll(Collection<? extends E> c) {
 return addAll(size, c);
 }
 
 /**
 	 * 将集合从指定位置开始插入
 	 * 
 	 * @param index
 	 * 在哪个索引处前插入指定集合中的第一个元素
 	 * @param c
 	 * 包含要添加到此链表中的元素的集合
 	 * @return {@code true} 如果该链表因添加而改变
 	 * @throws IndexOutOfBoundsException
 	 * {@inheritDoc}
 	 * @throws NullPointerException
 	 * 如果指定的集合是空的
 	 */
 public boolean addAll(int index, Collection<? extends E> c) {
 // 检查索引是否正确（0<=index<=size）
 checkPositionIndex(index);
 // 得到元素数组
 Object[] a = c.toArray();
 // 得到元素个数
 int numNew = a.length;
 // 没有元素，返回false
 if (numNew == 0)
 return false;
 // succ指向当前需要插入节点的位置，pred指向其前一个节点
 Node<E> pred, succ;
 // 末尾开始添加，当前节点后一个节点为null，前一个节点为尾节点
 if (index == size) {
 succ = null;
 pred = last;
 } else { 
 	//当前位置的节点为指定位置的节点，前一个节点为要添加的节点的前一个节点
 succ = node(index);
 pred = succ.prev;
 }
 // 遍历数组并添加到列表中
 for (Object o : a) {
 @SuppressWarnings("unchecked") E e = (E) o;
 // “封装”一个新节点
 Node<E> newNode = new Node<>(pred, e, null);
 // 原链表为null，新插入的节点作为链表首节点
 if (pred == null)
 first = newNode;
 else
 pred.next = newNode; // 存在前节点，前节点向后指向新加的节点
 pred = newNode; // pred指针向后移动
 }
 // 从最后开始添加，则新节点成为尾节点
 if (succ == null) {
 last = pred;
 } else {
 pred.next = succ; // 新节点向后指向之前得到的后续第一个节点
 succ.prev = pred; // 后续的第一个节点也应改为向前指向最后一个添加的节点
 }
 
 size += numNew;
 modCount++;
 return true;
 }
 
 /**
 	 * 删除所有元素
 	 */
 public void clear() {
 // 遍历链表，删除所有结点,方便gc回收垃圾
 for (Node<E> x = first; x != null; ) {
 Node<E> next = x.next;
 x.item = null;
 x.next = null;
 x.prev = null;
 x = next;
 }
 // 首尾结点置空
 first = last = null;
 // 元素数量置0
 size = 0;
 modCount++;
 }
 
 
 // 位置访问操作
 
 /**
 	 * 获取指定位置的元素
 	 * 
 	 * @param index
 	 * 要返回的元素的索引
 	 * @return 该链表中指定位置的元素
 	 * @throws IndexOutOfBoundsException
 	 * {@inheritDoc}
 	 */
 public E get(int index) {
 // 判断指定位置是否合法
 checkElementIndex(index);
 // 返回指定位置的元素
 return node(index).item;
 }
 
 /**
 	 * 修改指定位置的元素，返回之前元素
 	 * 
 	 * @param index
 	 * 要替换的元素的索引
 	 * @param element
 	 * 要存储在指定位置的元素
 	 * @return 之前在指定位置的元素
 	 * @throws IndexOutOfBoundsException
 	 * {@inheritDoc}
 	 */
 public E set(int index, E element) {
 // 判断指定位置是否合法
 checkElementIndex(index);
 // 获取指定位置的结点
 Node<E> x = node(index);
 // 获取该结点存储的元素
 E oldVal = x.item;
 // 修改该结点存储的元素
 x.item = element;
 // 返回该结点存储的之前的元素
 return oldVal;
 }
 
 /**
 	 * 在指定位置前插入指定元素
 	 * 头插法
 	 * @param index
 	 * 指定元素将被插入的索引
 	 * @param element
 	 * 要插入的元素
 	 * @throws IndexOutOfBoundsException
 	 * {@inheritDoc}
 	 */
 public void add(int index, E element) {
 // 判断指定位置是否合法
 checkPositionIndex(index);
 // 如果指定位置在尾部，则通过尾插法来插入指定元素
 if (index == size)
 linkLast(element);
 else // 如果指定位置不是尾部，则添加到指定位置前
 linkBefore(element, node(index));
 }
 
 /**
 	 * 删除指定位置的元素，返回之前元素
 	 * 
 	 * @param index
 	 * 要删除的元素的索引
 	 * @return 之前在指定位置的元素
 	 * @throws IndexOutOfBoundsException
 	 * {@inheritDoc}
 	 */
 public E remove(int index) {
 // 判断指定位置是否合法
 checkElementIndex(index);
 // 删除指定位置的结点，返回之前元素
 return unlink(node(index));
 }
 
 /**
 	 * 判断指定位置是否合法
 	 */
 private boolean isElementIndex(int index) {
 return index >= 0 && index < size;
 }
 
 /**
 	 * 判断迭代器遍历时或插入元素时指定位置是否合法
 	 */
 private boolean isPositionIndex(int index) {
 return index >= 0 && index <= size;
 }
 
 /**
 	 * 获取越界异常信息
 	 */
 private String outOfBoundsMsg(int index) {
 return "Index: " + index + ", Size: " + size;
 }
 
 /**
 	 * 判断指定位置是否合法
 	 * 
 	 * @param index
 	 */
 private void checkElementIndex(int index) {
 if (!isElementIndex(index))
 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
 }
 
 /**
 	 * 判断指定位置是否合法
 	 * 
 	 * @param index
 	 */
 private void checkPositionIndex(int index) {
 if (!isPositionIndex(index))
 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
 }
 
 /**
 	 * 获取指定下标的结点
 	 */
 Node<E> node(int index) {
 // 如果指定下标<一半元素数量，则从首结点开始遍历
 // 否则，从尾结点开始遍历
 if (index < (size >> 1)) {
 Node<E> x = first;
 for (int i = 0; i < index; i++)
 x = x.next;
 return x;
 } else {
 Node<E> x = last;
 for (int i = size - 1; i > index; i--)
 x = x.prev;
 return x;
 }
 }
 
 // 查询操作
 
 /**
 	 * 获取首次出现指定元素的位置 -1表示不存在
 	 * 同样是根据是否为null进行区分
 	 * @param o
 	 * 要查找的元素
 	 * @return the index of the first occurrence of the specified element in
 	 * this list, or -1 if this list does not contain the element
 	 */
 public int indexOf(Object o) {
 int index = 0;
 if (o == null) {
 // 遍历链表，顺序查找指定元素
 for (Node<E> x = first; x != null; x = x.next) {
 if (x.item == null)
 return index;
 index++;
 }
 } else {
 for (Node<E> x = first; x != null; x = x.next) {
 if (o.equals(x.item))
 return index;
 index++;
 }
 }
 return -1;
 }
 
 /**
 	 * 获取逆序下首次出现指定元素的位置 -1表示不存在
 	 * 
 	 * @param o
 	 * 要查找的元素
 	 * @return the index of the last occurrence of the specified element in this
 	 * list, or -1 if this list does not contain the element
 	 */
 public int lastIndexOf(Object o) {
 int index = size;
 if (o == null) {
 // 遍历链表，逆序查找指定元素
 for (Node<E> x = last; x != null; x = x.prev) {
 index--;
 if (x.item == null)
 return index;
 }
 } else {
 for (Node<E> x = last; x != null; x = x.prev) {
 index--;
 if (o.equals(x.item))
 return index;
 }
 }
 return -1;
 }
 
 // 队列操作
 
 /**
 	 * 出队（从前端），获得第一个元素，不存在会返回null，不会删除元素（节点） 获取首元素
 	 * 
 	 * @return the head of this list, or {@code null} 如果链表为空
 	 * @since 1.5
 	 */
 public E peek() {
 final Node<E> f = first;
 // 如果首结点为空，则返回null
 // 否则，返回首结点存储的元素
 return (f == null) ? null : f.item;
 }
 
 /**
 	 * 出队（从前端），不删除元素，若为null会抛出异常而不是返回null 获取首元素
 	 * 
 	 * @return the head of this list
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 * @since 1.5
 	 */
 public E element() {
 // 返回首结点存储的元素
 return getFirst();
 }
 
 /**
 	 * 出队（从前端），如果不存在会返回null，存在的话会返回值并移除这个元素（节点） 获取并删除首元素
 	 * 
 	 * @return the head of this list, or {@code null} 如果链表为空
 	 * @since 1.5
 	 */
 public E poll() {
 // 获取首结点引用
 final Node<E> f = first;
 // 如果首结点为空，则返回null
 // 否则，删除首结点，返回首结点存储的元素
 return (f == null) ? null : unlinkFirst(f);
 }
 
 /**
 	 * 出队（从前端），如果不存在会抛出异常而不是返回null，存在的话会返回值并移除这个元素（节点） 获取并删除首元素
 	 * 
 	 * @return the head of this list
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 * @since 1.5
 	 */
 public E remove() {
 // 删除首结点，返回首结点存储的元素
 return removeFirst();
 }
 
 /**
 	 * 入队（从后端），始终返回true
 	 * 
 	 * 链表不会溢出
 	 * @param e
 	 * the element to add
 	 * @return {@code true} (as specified by {@link Queue#offer})
 	 * @since 1.5
 	 */
 public boolean offer(E e) {
 // 通过尾插法插入指定元素，返回操作结果
 return add(e);
 }
 
 // 双端队列操作
 
 /**
 	 * 入队（从前端），始终返回true
 	 * 
 	 * @param e
 	 * 要插入的元素
 	 * @return {@code true} (as specified by {@link Deque#offerFirst})
 	 * @since 1.6
 	 */
 public boolean offerFirst(E e) {
 // 通过头插法来插入指定元素
 addFirst(e);
 return true;
 }
 
 /**
 	 * 入队（从后端），始终返回true
 	 * 
 	 * @param e
 	 * 要插入的元素
 	 * @return {@code true} (as specified by {@link Deque#offerLast})
 	 * @since 1.6
 	 */
 public boolean offerLast(E e) {
 // 通过尾插法来插入指定元素
 addLast(e);
 return true;
 }
 
 /**
 	 * 出队（从前端），获得第一个元素，不存在会返回null，不会删除元素（节点）
 	 * 
 	 * @return the first element of this list, or {@code null} 如果链表为空
 	 * @since 1.6
 	 */
 public E peekFirst() {
 // 获取首结点引用
 final Node<E> f = first;
 // 如果首结点为空，则返回null
 // 否则，返回首结点存储的元素
 return (f == null) ? null : f.item;
 }
 
 /**
 	 * 出队（从后端），获得最后一个元素，不存在会返回null，不会删除元素（节点）
 	 * 
 	 * @return the last element of this list, or {@code null} 如果链表为空
 	 * @since 1.6
 	 */
 public E peekLast() {
 // 获取尾结点引用
 final Node<E> l = last;
 // 如果尾结点为空，则返回null
 // 否则，返回尾结点存储的元素
 return (l == null) ? null : l.item;
 }
 
 /**
 	 * 出队（从前端），获得第一个元素，不存在会返回null，会删除元素（节点）
 	 * 
 	 * @return the first element of this list, or {@code null} if this list is
 	 * empty
 	 * @since 1.6
 	 */
 public E pollFirst() {
 // 获取首结点引用
 final Node<E> f = first;
 // 如果首结点为空，则返回null
 // 否则，删除首结点，返回首结点存储的元素
 return (f == null) ? null : unlinkFirst(f);
 }
 
 /**
 	 * 出队（从后端），获得最后一个元素，不存在会返回null，会删除元素（节点）
 	 * 
 	 * @return the last element of this list, or {@code null} if this list is
 	 * empty
 	 * @since 1.6
 	 */
 public E pollLast() {
 // 获取尾结点引用
 final Node<E> l = last;
 // 如果尾结点为空，则返回null
 // 否则，删除尾结点，返回尾结点存储的元素
 return (l == null) ? null : unlinkLast(l);
 }
 
 /**
 	 * 入栈，从前面添加
 	 * 
 	 * @param e
 	 * the element to push
 	 * @since 1.6
 	 */
 public void push(E e) {
 // 通过头插法来插入指定元素
 addFirst(e);
 }
 
 /**
 	 * 出栈，返回栈顶元素，从前面移除（会删除）
 	 * 
 	 * @return the element at the front of this list (which is the top of the
 	 * stack represented by this list)
 	 * @throws NoSuchElementException
 	 * 如果链表为空
 	 * @since 1.6
 	 */
 public E pop() {
 // 删除首结点，返回首结点存储的元素
 return removeFirst();
 }
 
 /**
 	 * 删除顺序下首次出现的指定元素，返回操作结果
 	 * 
 	 * @param o
 	 * 要从该列表中删除的元素（如果存在）
 	 * @return {@code true} 如果链表包含指定的元素
 	 * @since 1.6
 	 */
 public boolean removeFirstOccurrence(Object o) {
 // 删除顺序下首次出现的指定元素对应的结点，返回操作结果
 return remove(o);
 }
 
 /**
 	 * 删除逆序下首次出现的指定元素，返回操作结果
 	 * 
 	 * @param o
 	 * 要从该列表中删除的元素（如果存在）
 	 * @return {@code true} 如果链表包含指定的元素
 	 * @since 1.6
 	 */
 public boolean removeLastOccurrence(Object o) {
 // 由于LinkedList中允许存放null，因此下面通过两种情况来分别处理
 if (o == null) {
 // 遍历链表，从尾结点开始查找指定元素
 // 如果查找成功，删除该结点，返回true
 for (Node<E> x = last; x != null; x = x.prev) {
 if (x.item == null) {
 unlink(x);
 return true;
 }
 }
 } else {
 for (Node<E> x = last; x != null; x = x.prev) {
 if (o.equals(x.item)) {
 unlink(x);
 return true;
 }
 }
 }
 // 查找失败
 return false;
 }
 
 /**
 	 * Returns a list-iterator of the elements in this list (in proper
 	 * sequence), starting at the specified position in the list. Obeys the
 	 * general contract of {@code List.listIterator(int)}.
 	 * 
 	 * 
 	 * The list-iterator is fail-fast: if the list is structurally
 	 * modified at any time after the Iterator is created, in any way except
 	 * through the list-iterator's own {@code remove} or {@code add} methods,
 	 * the list-iterator will throw a {@code ConcurrentModificationException}.
 	 * Thus, in the face of concurrent modification, the iterator fails quickly
 	 * and cleanly, rather than risking arbitrary, non-deterministic behavior at
 	 * an undetermined time in the future.
 	 * 
 	 * @param index
 	 * index of the first element to be returned from the
 	 * list-iterator (by a call to {@code next})
 	 * @return a ListIterator of the elements in this list (in proper sequence),
 	 * starting at the specified position in the list
 	 * @throws IndexOutOfBoundsException
 	 * {@inheritDoc}
 	 * @see List#listIterator(int)
 	 */
 public ListIterator<E> listIterator(int index) {
 checkPositionIndex(index);
 return new ListItr(index);
 }
 
 private class ListItr implements ListIterator<E> {
 private Node<E> lastReturned;
 private Node<E> next;
 private int nextIndex;
 private int expectedModCount = modCount;
 
 ListItr(int index) {
 // assert isPositionIndex(index);
 next = (index == size) ? null : node(index);
 nextIndex = index;
 }
 
 public boolean hasNext() {
 return nextIndex < size;
 }
 
 public E next() {
 checkForComodification();
 if (!hasNext())
 throw new NoSuchElementException();
 
 lastReturned = next;
 next = next.next;
 nextIndex++;
 return lastReturned.item;
 }
 
 public boolean hasPrevious() {
 return nextIndex > 0;
 }
 
 public E previous() {
 checkForComodification();
 if (!hasPrevious())
 throw new NoSuchElementException();
 
 lastReturned = next = (next == null) ? last : next.prev;
 nextIndex--;
 return lastReturned.item;
 }
 
 public int nextIndex() {
 return nextIndex;
 }
 
 public int previousIndex() {
 return nextIndex - 1;
 }
 
 public void remove() {
 checkForComodification();
 if (lastReturned == null)
 throw new IllegalStateException();
 
 Node<E> lastNext = lastReturned.next;
 unlink(lastReturned);
 if (next == lastReturned)
 next = lastNext;
 else
 nextIndex--;
 lastReturned = null;
 expectedModCount++;
 }
 
 public void set(E e) {
 if (lastReturned == null)
 throw new IllegalStateException();
 checkForComodification();
 lastReturned.item = e;
 }
 
 public void add(E e) {
 checkForComodification();
 lastReturned = null;
 if (next == null)
 linkLast(e);
 else
 linkBefore(e, next);
 nextIndex++;
 expectedModCount++;
 }
 
 public void forEachRemaining(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 while (modCount == expectedModCount && nextIndex < size) {
 action.accept(next.item);
 lastReturned = next;
 next = next.next;
 nextIndex++;
 }
 checkForComodification();
 }
 
 final void checkForComodification() {
 if (modCount != expectedModCount)
 throw new ConcurrentModificationException();
 }
 }
 
 /**
 	 * 节点的数据结构，包含前后节点的引用和当前节点
 	 * 
 	 * @param <E>
 	 */
 private static class Node<E> {
 // 存储的元素
 E item;
 // 后继结点
 Node<E> next;
 // 前驱结点
 Node<E> prev;
 
 // 前驱结点、存储的元素和后继结点作为参数的构造方法
 Node(Node<E> prev, E element, Node<E> next) {
 this.item = element;
 this.next = next;
 this.prev = prev;
 }
 }
 
 /**
 	 * 返回迭代器
 	 * 
 	 * @since 1.6
 	 */
 public Iterator<E> descendingIterator() {
 return new DescendingIterator();
 }
 
 /**
 	 * 因为采用链表实现，所以迭代器很简单
 	 */
 private class DescendingIterator implements Iterator<E> {
 private final ListItr itr = new ListItr(size());
 
 public boolean hasNext() {
 return itr.hasPrevious();
 }
 
 public E next() {
 return itr.previous();
 }
 
 public void remove() {
 itr.remove();
 }
 }
 
 /**
 	 * 父类克隆方法
 	 */
 @SuppressWarnings("unchecked")
 private LinkedList<E> superClone() {
 try {
 return (LinkedList<E>) super.clone();
 } catch (CloneNotSupportedException e) {
 throw new InternalError(e);
 }
 }
 
 /**
 	 * 克隆，浅拷贝
 	 * 
 	 * 浅拷贝时，若存储的是对象的引用，拷贝时，对象本身的改变将表现到副本中，而深拷贝不会。
 	 * @return a shallow copy of this {@code LinkedList} instance
 	 */
 public Object clone() {
 LinkedList<E> clone = superClone();
 
 // 链表初始化
 clone.first = clone.last = null;
 clone.size = 0;
 clone.modCount = 0;
 
 // 插入结点
 for (Node<E> x = first; x != null; x = x.next)
 clone.add(x.item);
 // 返回克隆后的对象引用
 return clone;
 }
 
 /**
 * 返回新的数组，数组含有列表中所有元素
 	 */
 public Object[] toArray() {
 Object[] result = new Object[size];
 int i = 0;
 for (Node<E> x = first; x != null; x = x.next)
 result[i++] = x.item;
 return result;
 }
 
 /**
 	 * Returns an array containing all of the elements in this list in proper
 	 * sequence (from first to last element); the runtime type of the returned
 	 * array is that of the specified array. If the list fits in the specified
 	 * array, it is returned therein. Otherwise, a new array is allocated with
 	 * the runtime type of the specified array and the size of this list.
 	 * 
 	 * 
 	 * If the list fits in the specified array with room to spare (i.e., the
 	 * array has more elements than the list), the element in the array
 	 * immediately following the end of the list is set to {@code null}. (This
 	 * is useful in determining the length of the list only if the
 	 * caller knows that the list does not contain any null elements.)
 	 * 
 	 * 
 	 * Like the {@link #toArray()} method, this method acts as bridge between
 	 * array-based and collection-based APIs. Further, this method allows
 	 * precise control over the runtime type of the output array, and may, under
 	 * certain circumstances, be used to save allocation costs.
 	 * 
 	 * 
 	 * Suppose {@code x} is a list known to contain only strings. The following
 	 * code can be used to dump the list into a newly allocated array of
 	 * {@code String}:
 	 * 
 	 * 
 	 * <pre>
 	 * String[] y = x.toArray(new String[0]);
 	 * </pre>
 	 * 
 	 * 
 	 * Note that {@code toArray(new Object[0])} is identical in function to
 	 * {@code toArray()}.
 	 * 
 	 * @param a
 	 * the array into which the elements of the list are to be
 	 * stored, if it is big enough; otherwise, a new array of the
 	 * same runtime type is allocated for this purpose.
 	 * @return an array containing the elements of the list
 	 * @throws ArrayStoreException
 	 * if the runtime type of the specified array is not a supertype
 	 * of the runtime type of every element in this list
 	 * @throws NullPointerException
 	 * if the specified array is null
 	 */
 @SuppressWarnings("unchecked")
 public <T> T[] toArray(T[] a) {
 if (a.length < size)
 a = (T[]) java.lang.reflect.Array.newInstance(
 a.getClass().getComponentType(), size);
 int i = 0;
 Object[] result = a;
 for (Node<E> x = first; x != null; x = x.next)
 result[i++] = x.item;
 
 if (a.length > size)
 a[size] = null;
 
 return a;
 }
 
 private static final long serialVersionUID = 876323262645176354L;
 
 /**
 	 * 序列化
 	 */
 private void writeObject(java.io.ObjectOutputStream s)
 throws java.io.IOException {
 // 默认序列化
 s.defaultWriteObject();
 
 // 写入元素数量
 s.writeInt(size);
 
 // 遍历链表，写入所有元素
 for (Node<E> x = first; x != null; x = x.next)
 s.writeObject(x.item);
 }
 
 /**
 	 * 反序列化
 	 */
 @SuppressWarnings("unchecked")
 private void readObject(java.io.ObjectInputStream s)
 throws java.io.IOException, ClassNotFoundException {
 // 默认反序列化
 s.defaultReadObject();
 
 // 读取元素数量
 int size = s.readInt();
 
 // 遍历链表，读取所有元素并尾部插入
 for (int i = 0; i < size; i++)
 linkLast((E) s.readObject());
 }
 
 /**
 	 * Creates a <a href="Spliterator.html#binding">late-binding</a>
 	 * and fail-fast {@link Spliterator} over the elements in this
 	 * list.
 	 * 
 	 * 
 	 * The {@code Spliterator} reports {@link Spliterator#SIZED} and
 	 * {@link Spliterator#ORDERED}. Overriding implementations should document
 	 * the reporting of additional characteristic values.
 	 * 
 	 * @return a {@code Spliterator} over the elements in this list
 	 * @implNote The {@code Spliterator} additionally reports
 	 * {@link Spliterator#SUBSIZED} and implements {@code trySplit} to
 	 * permit limited parallelism..
 	 * @since 1.8
 	 */
 @Override
 public Spliterator<E> spliterator() {
 return new LLSpliterator<E>(this, -1, 0);
 }
 
 /**
 	 * A customized variant of Spliterators.IteratorSpliterator
 	 */
 static final class LLSpliterator<E> implements Spliterator<E> {
 static final int BATCH_UNIT = 1 << 10; // batch array size increment
 static final int MAX_BATCH = 1 << 25; // max batch array size;
 final LinkedList<E> list; // null OK unless traversed
 Node<E> current; // current node; null until initialized
 int est; // size estimate; -1 until first needed
 int expectedModCount; // initialized when est set
 int batch; // batch size for splits
 
 LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {
 this.list = list;
 this.est = est;
 this.expectedModCount = expectedModCount;
 }
 
 final int getEst() {
 int s; // force initialization
 final LinkedList<E> lst;
 if ((s = est) < 0) {
 if ((lst = list) == null)
 s = est = 0;
 else {
 expectedModCount = lst.modCount;
 current = lst.first;
 s = est = lst.size;
 }
 }
 return s;
 }
 
 public long estimateSize() {
 return (long) getEst();
 }
 
 public Spliterator<E> trySplit() {
 Node<E> p;
 int s = getEst();
 if (s > 1 && (p = current) != null) {
 int n = batch + BATCH_UNIT;
 if (n > s)
 n = s;
 if (n > MAX_BATCH)
 n = MAX_BATCH;
 Object[] a = new Object[n];
 int j = 0;
 do {
 a[j++] = p.item;
 } while ((p = p.next) != null && j < n);
 current = p;
 batch = j;
 est = s - j;
 return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);
 }
 return null;
 }
 
 public void forEachRemaining(Consumer<? super E> action) {
 Node<E> p;
 int n;
 if (action == null) throw new NullPointerException();
 if ((n = getEst()) > 0 && (p = current) != null) {
 current = null;
 est = 0;
 do {
 E e = p.item;
 p = p.next;
 action.accept(e);
 } while (p != null && --n > 0);
 }
 if (list.modCount != expectedModCount)
 throw new ConcurrentModificationException();
 }
 
 public boolean tryAdvance(Consumer<? super E> action) {
 Node<E> p;
 if (action == null) throw new NullPointerException();
 if (getEst() > 0 && (p = current) != null) {
 --est;
 E e = p.item;
 current = p.next;
 action.accept(e);
 if (list.modCount != expectedModCount)
 throw new ConcurrentModificationException();
 return true;
 }
 return false;
 }
 
 public int characteristics() {
 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
 }
 }
 
 }

[Link 1]: http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Queue.html
[Link 2]: http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Deque.html
[Collections.synchronizedList]: http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/Collections.html#synchronizedList%28java.util.List%29
[ConcurrentModificationException]: http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/ConcurrentModificationException.html