blocks|key|406945|text|它们之间没有区别，文档中也列出了这一点，但您必须进行一些递归搜索才能到达那里。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|406946|LinkedList实现了两个接口--+Queue和Deque。Deque是从Queue扩展而来的。|offset|length|style|CODE|406947|现在，Deque已经定义了方法-+Deque#pollFirst()并继承了方法-+Queue#poll()。|406948|因此，LinkedList基本上为它实现的两个接口定义了这两个方法。|406949|关于这两种方法之间的相似性，在Deque的文档中列出如下：|406950|406951|此接口扩展了Queue接口。将双队列用作队列时，会产生FIFO+(先进先出)行为。元素被添加到双队列的末尾，并从开头删除。从Queue接口继承的方法完全等同于Deque方法，如下表所示：|blockquote|406952|406953|406954|并且有一个表列出了Queue类的方法和等效的Deque方法。参见Deque#poll()，Deque#peek()，例如，他们清楚地列出了等价的方法。|406955|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/util/LinkedList.html|1|http://docs.oracle.com/javase/7/docs/api/java/util/Queue.html|2|http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html|3|http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#pollFirst%2528%2529|4|http://docs.oracle.com/javase/7/docs/api/java/util/Queue.html#poll%2528%2529|5|6|http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#poll%2528%2529|7|http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#peek%2528%2529^0|0|0|A|K|5|Q|5|W|5|13|5|0|A|0|K|5|1|Q|5|2|0|3|5|H|H|16|C|H|H|3|16|C|4|0|3|A|0|F|5|F|5|5|0|0|0|0|0|9|5|M|5|W|C|19|C|W|C|6|19|C|7|0^^$0|@$1|2|3|4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1H|8|@$D|1I|E|1J|F|G]|$D|1K|E|1L|F|G]|$D|1M|E|1N|F|G]|$D|1O|E|1P|F|G]|$D|1Q|E|1R|F|G]]|9|@$D|1S|E|1T|1|1U]|$D|1V|E|1W|1|1X]|$D|1Y|E|1Z|1|20]]|A|$]]|$1|H|3|I|5|6|7|21|8|@$D|22|E|23|F|G]|$D|24|E|25|F|G]|$D|26|E|27|F|G]]|9|@$D|28|E|29|1|2A]|$D|2B|E|2C|1|2D]]|A|$]]|$1|J|3|K|5|6|7|2E|8|@$D|2F|E|2G|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|2H|8|@$D|2I|E|2J|F|G]]|9|@$D|2K|E|2L|1|2M]]|A|$]]|$1|N|3|-4|5|6|7|2N|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|2O|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|2P|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|2Q|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|2R|8|@$D|2S|E|2T|F|G]|$D|2U|E|2V|F|G]|$D|2W|E|2X|F|G]|$D|2Y|E|2Z|F|G]]|9|@$D|30|E|31|1|32]|$D|33|E|34|1|35]]|A|$]]|$1|V|3|-4|5|6|7|36|8|@]|9|@]|A|$]]]|W|$X|$5|Y|Z|10|A|$11|12]]|13|$5|Y|Z|10|A|$11|14]]|15|$5|Y|Z|10|A|$11|16]]|17|$5|Y|Z|10|A|$11|18]]|19|$5|Y|Z|10|A|$11|1A]]|1B|$5|Y|Z|10|A|$11|16]]|1C|$5|Y|Z|10|A|$11|1D]]|1E|$5|Y|Z|10|A|$11|1F]]]]

There is no difference between them, and it is listed in the documentation too, but you have to do some recursive searching to get there.

<a href="http://docs.oracle.com/javase/7/docs/api/java/util/LinkedList.html"><code>LinkedList</code></a> implements two interfaces - <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Queue.html"><code>Queue</code></a> and <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html"><code>Deque</code></a>. And <code>Deque</code> extends from <code>Queue</code>. 

Now, <code>Deque</code> has defined the method - <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#pollFirst%28%29"><code>Deque#pollFirst()</code></a> and inherited the method - <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Queue.html#poll%28%29"><code>Queue#poll()</code></a>. 

So, <code>LinkedList</code> has basically these two methods defined for the two interfaces it implements. 

And about the similarity between those two methods, it is listed in documentation of <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html"><code>Deque</code></a> as:

<blockquote>
 This interface extends the Queue interface. When a deque is used as a
 queue, FIFO (First-In-First-Out) behavior results. Elements are added
 at the end of the deque and removed from the beginning. The methods
 inherited from the Queue interface are precisely equivalent to Deque
 methods as indicated in the following table:
</blockquote>

And there is a table listing the methods of <code>Queue</code> class and the equivalent <code>Deque</code> method. See <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#poll%28%29"><code>Deque#poll()</code></a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Deque.html#peek%28%29"><code>Deque#peek()</code></a> for e.g. They clearly list the equivalent method.

blocks|key|409868|text|你说的对，这是错误的文档或者别的什么。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|409869|peek()检索这个列表的头部(第一个元素)，但不删除。|409870|peekFirst()检索但不删除该列表的第一个元素，如果该列表为空，则返回null。|409871|这就是它所说的，我在我的Java书中读到，head是列表中的第一个项目。|409872|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Your right it's bad documentation or something.

peek()
Retrieves, but does not remove, the head (first element) of this list.

peekFirst()
Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.

This is what it says and I'm read here in my Java book that the head is the first item in a list.

Are there any differences between different methods in each of the following groups of element retrieve operations in <code>LinkedList</code>?

Returning null + removing operations: <code>poll()</code>, <code>pollFirst()</code>.

Returning null + not removing operations: <code>peek()</code>, <code>peekFirst()</code>.

Throwing exception + removing operations: <code>pop()</code>, <code>remove()</code>, <code>removeFirst()</code>.

Throwing exception + not removing operations: <code>element()</code>, <code>getFirst()</code>.

Similar duplications exists in insertion methods. 

If there is no such difference, I would expect it to be mentioned in the javadoc of the methods (something like the good old "This is exactly like calling ..."). Is it only a sloppy documentation, or am I missing anything?

Java LinkedList - differences between retrieve operations

Java

在LinkedList中，以下每组元素检索操作中的不同方法之间是否存在差异返回null +删除操作： poll()，pollFirst()。返回null +未移除操作： peek()，peekFirst()。抛出异常+移除操作： pop()，remove()，removeFirst()。抛出异常+未移除操作： elem...

问Java LinkedList -检索操作之间的区别
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