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java常用操作总结.html
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</style><title>java常用操作总结</title>
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<div id='write' class=''><h1 id='自己的一些常用java-总结'><span>自己的一些常用Java 总结</span></h1><div class='md-toc' mdtype='toc'><p class="md-toc-content" role="list"><span role="listitem" class="md-toc-item md-toc-h1" data-ref="n0"><a class="md-toc-inner" href="#自己的一些常用java-总结">自己的一些常用Java 总结</a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n4"><a class="md-toc-inner" href="#hashmap-map"><strong>HashMap Map</strong></a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n45"><a class="md-toc-inner" href="#arraydeque-和-linkedlist">ArrayDeque 和 LinkedList</a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n53"><a class="md-toc-inner" href="#string的用法"><strong>String的用法</strong></a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n60"><a class="md-toc-inner" href="#stack-堆栈">STACK 堆栈</a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n83"><a class="md-toc-inner" href="#set">Set</a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n126"><a class="md-toc-inner" href="#动态数组-arraylist"><strong>动态数组 ArrayList</strong></a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n185"><a class="md-toc-inner" href="#iterator-接口"><strong>Iterator 接口</strong></a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n200"><a class="md-toc-inner" href="#linkedlist"><strong>LinkedList</strong></a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n230"><a class="md-toc-inner" href="#优先队列priorityqueue">优先队列PriorityQueue</a></span><span role="listitem" class="md-toc-item md-toc-h3" data-ref="n239"><a class="md-toc-inner" href="#关于拆箱和装箱"><strong>关于拆箱和装箱</strong></a></span></p></div><p><span>总是忘记所以被迫总结</span>😄</p><h3 id='hashmap-map'><strong><span>HashMap Map</span></strong></h3><blockquote><p><span>HashMap 是一个散列表，它存储的内容是键值对(key-value)映射。</span></p><p><span>HashMap 实现了 Map 接口，根据键的 HashCode 值存储数据，具有很快的访问速度，最多允许一条记录的键为 null，</span><strong><span>不支持线程同步</span></strong><span>。</span></p><p><span>HashMap 实现了 Map 接口，根据键的 HashCode 值存储数据，具有很快的访问速度，最多允许一条记录的键为 null，不支持线程同步。</span></p></blockquote><p><span>HashMap 的 </span><strong><span>key</span></strong><span> 与 </span><strong><span>value 类型</span></strong><span>可以相同也可以不同，可以是字符串（String）类型的 key 和 value，也可以是整型（Integer）的 key 和字符串（String）类型的 value。</span></p><p><img src="https://s2.loli.net/2023/04/16/4tmxeNMBqOvkjHf.png" alt="image-20230416233759898" style="zoom: 80%;" /></p><figure><table><thead><tr><th style='text-align:left;' ><span>基本类型</span></th><th style='text-align:left;' ><span>引用类型</span></th></tr></thead><tbody><tr><td style='text-align:left;' ><span>boolean</span></td><td style='text-align:left;' ><span>Boolean</span></td></tr><tr><td style='text-align:left;' ><span>byte</span></td><td style='text-align:left;' ><span>Byte</span></td></tr><tr><td style='text-align:left;' ><span>short</span></td><td style='text-align:left;' ><span>Short</span></td></tr><tr><td style='text-align:left;' ><span>int</span></td><td style='text-align:left;' ><span>Integer</span></td></tr><tr><td style='text-align:left;' ><span>long</span></td><td style='text-align:left;' ><span>Long</span></td></tr><tr><td style='text-align:left;' ><span>float</span></td><td style='text-align:left;' ><span>Float</span></td></tr><tr><td style='text-align:left;' ><span>double</span></td><td style='text-align:left;' ><span>Double</span></td></tr><tr><td style='text-align:left;' ><span>char</span></td><td style='text-align:left;' ><span>Character</span></td></tr></tbody></table></figure><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang="" style="break-inside: unset;"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang=""><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 49px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 41px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>16</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -41px; width: 41px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 32px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">import java.util.HashMap; // 引入 HashMap 类</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">HashMap<Integer, String> Sites = new HashMap<Integer, String>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>// 创建 HashMap 对象 Sites</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> HashMap<Integer, String> Sites = new HashMap<Integer, String>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> // 添加键值对</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">6</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> Sites.put(1, "Google");</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">7</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> Sites.put(2, "Runoob");</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">8</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> Sites.put(3, "Taobao");</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">9</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> Sites.put(4, "Zhihu");</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 32px;">10</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> System.out.println(Sites);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">11</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">//结果</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">12</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">{1=Google, 2=Runoob, 3=Taobao, 4=Zhihu}</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">13</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">containsKey(K） - 检查指定的键K是否在map中。</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">14</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="" cm-zwsp="">
</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 32px;">15</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">containsValue(V) - 检查指定的值V是否存在于map中。</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -41px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 32px;">16</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">get(K) - 返回与指定键K关联的值。如果找不到该键，则返回null。</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 518px;"></div><div class="CodeMirror-gutters" style="height: 518px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 40px;"></div></div></div></div></pre><blockquote><p><span>具体其他的可以参考这个</span><a href='[Java HashMap | 菜鸟教程 (runoob.com)](https://www.runoob.com/java/java-hashmap.html)'><span>Java Map菜鸟</span></a></p><p><a href='[Java Stack（堆栈） - Java教程 - 菜鸟教程 (cainiaojc.com)](https://www.cainiaojc.com/java/java-stack.html)'><span>菜鸟教程里面有对应的类集成图</span></a></p></blockquote><hr /><p> </p><h3 id='arraydeque-和-linkedlist'><span>ArrayDeque 和 LinkedList</span></h3><blockquote><p><a href='https://juejin.cn/post/7162819765361672199'><span>在数据结构上，ArrayDeque 和 LinkedList 都实现了 Java Deque 双端队列接口。但 ArrayDeque 没有实现了 Java List 列表接口，所以不具备根据索引位置操作的行为。ArrayDeque 和 LinkedList 都不考虑线程同步，不保证线程安全</span></a><a href='https://juejin.cn/post/7162819765361672199'><span>1</span></a><span>。</span></p><p><a href='https://leetcode.cn/circle/article/bXc4tx/'><span>ArrayDeque 基于数组实现双端队列，而 LinkedList 基于双向链表实现双端队列。数组采用连续的内存地址空间，通过下标索引访问，链表是非连续的内存地址空间，通过指针访问。所以在寻址方面数组的效率高于链表</span></a><a href='https://leetcode.cn/circle/article/bXc4tx/'><span>2</span></a><span>。</span></p><p><span>更多的还有一些关于地址变换的问题。</span></p></blockquote><p> </p><hr /><p> </p><h3 id='string的用法'><strong><span>String的用法</span></strong></h3><blockquote><p><span>一个问题困扰我很久：Java中，字符串是一个对象不是一个字符数组，因此不能使用数组索引来访问元素，C++中可以。Java中采用的事charAt()访问单个字符。</span></p></blockquote><p><span>注意：String[]是创建一个</span><strong><span>字符串</span></strong><span> 数组，每项都是一个字符串，是一个对象，比如{"张三"，"李四"}</span></p><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang=""><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang=""><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>1</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">char ch = s.charAt(i);</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 29px;"></div><div class="CodeMirror-gutters" style="height: 29px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre><hr /><p> </p><h3 id='stack-堆栈'><span>STACK 堆栈</span></h3><blockquote><p><span>建立</span><code>Stack<Type> stacks =new Stack<>();</code></p><p><span>常用函数：</span><code>push,pop,peek()//会返回对象,search()//同理返回对象,empty()</code></p><p><strong><span>使用ArrayDeque 代替 Stack</span></strong><span> </span></p><p><span>本Stack类提供直接执行堆栈的数据结构。但是，建议不要使用它。而是使用ArrayDeque类（实现Deque接口）在Java中实现堆栈数据结构。</span></p><p><strong><span>Stack类只有empty(),Deque才有isEmpty()</span></strong></p></blockquote><p><span> </span><strong><span>ArrayDeque作为堆栈</span></strong></p><p><span>要在Java中实现</span><strong><span>LIFO（后进先出）</span></strong><span>堆栈，建议在</span><a href='https://www.cainiaojc.com/java/java-stack.html'><span>Stack类</span></a><span>上使用双端队列。该ArrayDeque类比</span><strong><span>Stack类快</span></strong><span>。Java Collections框架的Stack类提供了堆栈的实现。但是，建议Deque用作堆栈而不是</span><a href='https://www.cainiaojc.com/java/java-stack.html'><span>Stack类</span></a><span>。这是因为Stack的方法是同步的。</span></p><p><img src="https://s2.loli.net/2023/04/17/erUfZpnw6VON2Cz.png" referrerpolicy="no-referrer" alt="image-20230417172243579"></p><p><span>ArrayDeque 提供了以下可用于实现堆栈的方法。</span></p><p><code>ArrayDeque<T> stack = new ArrayDeque<>();</code></p><blockquote><ul><li><p><span>push() - 在堆栈顶部添加一个元素</span></p></li><li><p><span>peek() - 从堆栈顶部返回一个元素</span></p></li><li><p><span>pop() - 返回并从堆栈顶部删除元素</span></p></li></ul></blockquote><p><span>数组问题Arrays</span></p><blockquote><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>1</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">int</span> <span class="cm-variable">arrayLength</span> <span class="cm-operator">=</span> <span class="cm-variable">number</span>.<span class="cm-variable">length</span>;</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 29px;"></div><div class="CodeMirror-gutters" style="height: 29px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre></blockquote><h3 id='set'><span>Set</span></h3><p><span>由于Set是接口，因此无法从中创建对象。</span></p><p><span>为了使用Set接口的功能，我们可以使用以下类：</span></p><ul><li><p><a href='https://www.cainiaojc.com/java/java-hashset.html'><span>HashSet</span></a></p></li><li><p><a href='https://www.cainiaojc.com/java/java-linkedhashset.html'><span>LinkedHashSet</span></a></p></li><li><p><a href='https://www.cainiaojc.com/java/java-enumset.html'><span>EnumSet</span></a></p></li><li><p><a href='https://www.cainiaojc.com/java/java-treeset.html'><span>TreeSet</span></a></p></li></ul><p><span>这些类在Collections框架中定义并实现Set接口</span></p><p><span>Set的一些方法：</span></p><p><span>Set接口包含Collection接口的所有方法。 这是因为Collection是Set的超级接口。</span></p><p><span>Set接口中还提供了Collection接口的一些常用方法：</span></p><blockquote><ul><li><p><strong><span>add()</span></strong><span> - 将指定的元素添加到集合中</span></p></li><li><p><strong><span>addAll()</span></strong><span> - 将指定集合的所有元素添加到集合中</span></p></li><li><p><strong><span>iterator()</span></strong><span> -返回一个迭代器，该迭代器可用于顺序访问集合中的元素</span></p></li><li><p><strong><span>remove()</span></strong><span> - 从集合中移除指定的元素</span></p></li><li><p><strong><span>removeAll()</span></strong><span> - 从存在于另一个指定集合中的集合中删除所有元素</span></p></li><li><p><strong><span>keepAll()</span></strong><span> -保留集合中所有还存在于另一个指定集合中的所有元素</span></p></li><li><p><strong><span>clear()</span></strong><span> - 从集合中删除所有元素</span></p></li><li><p><strong><span>size()</span></strong><span> - 返回集合的长度（元素数）</span></p></li><li><p><strong><span>toArray()</span></strong><span> - 返回包含集合中所有元素的数组</span></p></li><li><p><strong><span>contains()</span></strong><span> - 如果集合包含指定的元素，则返回true</span></p></li><li><p><strong><span>containsAll()</span></strong><span> - 如果集合包含指定集合的所有元素，则返回true</span></p></li><li><p><strong><span>hashCode()</span></strong><span> -返回哈希码值（集合中元素的地址）</span></p></li></ul></blockquote><hr /><h3 id='动态数组-arraylist'><strong><span>动态数组 ArrayList</span></strong></h3><p><span>ArrayList 类是一个可以动态修改的数组，与普通数组的区别就是它是没有固定大小的限制，我们可以添加或删除元素。</span></p><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang=""><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang=""><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>2</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">import java.util.ArrayList; // 引入 ArrayList 类</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">ArrayList<E> objectName =new ArrayList<>(); // 初始化</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 58px;"></div><div class="CodeMirror-gutters" style="height: 58px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre><p><span>Java ArrayList 常用方法列表如下：</span></p><figure><table><thead><tr><th style='text-align:left;' ><span>方法</span></th><th style='text-align:left;' ><span>描述</span></th></tr></thead><tbody><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-add.html'><span>add()</span></a></td><td style='text-align:left;' ><span>将元素插入到指定位置的 arraylist 中</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-addall.html'><span>addAll()</span></a></td><td style='text-align:left;' ><span>添加集合中的所有元素到 arraylist 中</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-clear.html'><span>clear()</span></a></td><td style='text-align:left;' ><span>删除 arraylist 中的所有元素</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-clone.html'><span>clone()</span></a></td><td style='text-align:left;' ><span>复制一份 arraylist</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-contains.html'><span>contains()</span></a></td><td style='text-align:left;' ><span>判断元素是否在 arraylist</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-get.html'><span>get()</span></a></td><td style='text-align:left;' ><span>通过索引值获取 arraylist 中的元素</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-indexof.html'><span>indexOf()</span></a></td><td style='text-align:left;' ><span>返回 arraylist 中元素的索引值</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-removeall.html'><span>removeAll()</span></a></td><td style='text-align:left;' ><span>删除存在于指定集合中的 arraylist 里的所有元素</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-remove.html'><span>remove()</span></a></td><td style='text-align:left;' ><span>删除 arraylist 里的单个元素</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-size.html'><span>size()</span></a></td><td style='text-align:left;' ><span>返回 arraylist 里元素数量</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-isempty.html'><span>isEmpty()</span></a></td><td style='text-align:left;' ><span>判断 arraylist 是否为空</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-sublist.html'><span>subList()</span></a></td><td style='text-align:left;' ><span>截取部分 arraylist 的元素</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-set.html'><span>set()</span></a></td><td style='text-align:left;' ><span>替换 arraylist 中指定索引的元素</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-sort.html'><span>sort()</span></a></td><td style='text-align:left;' ><span>对 arraylist 元素进行排序</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-toarray.html'><span>toArray()</span></a></td><td style='text-align:left;' ><span>将 arraylist 转换为数组</span></td></tr><tr><td style='text-align:left;' ><a href='https://www.runoob.com/java/java-arraylist-tostring.html'><span>toString()</span></a></td><td style='text-align:left;' ><span>将 arraylist 转换为字符串</span></td></tr></tbody></table></figure><p><span>Java Comparator 接口的 naturalOrder() 方法指定元素以自然顺序（升序）排序。</span></p><p><code>sites.sort(Comparator.reverseOrder());</code></p><hr /><h3 id='iterator-接口'><strong><span>Iterator 接口</span></strong></h3><blockquote><p><span>Iterator接口提供了4种方法，可用于对集合元素执行各种操作。</span></p><ul><li><p><span>hasNext() - 如果集合中存在元素，则返回true</span></p></li><li><p><span>next() - 返回集合的下一个元素</span></p></li><li><p><span>remove() -删除next()返回的最后一个元素</span></p></li><li><p><span>forEachRemaining() - 对集合的每个剩余元素执行指定的操作</span></p></li></ul></blockquote><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>2</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">ArrayList</span><span class="cm-operator"><</span><span class="cm-variable-3">Integer</span><span class="cm-operator">></span> <span class="cm-variable">numbers</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">ArrayList</span><span class="cm-operator"><></span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">Iterator</span><span class="cm-operator"><</span><span class="cm-variable-3">Integer</span><span class="cm-operator">></span> <span class="cm-variable">iterate</span> <span class="cm-operator">=</span> <span class="cm-variable">numbers</span>.<span class="cm-variable">iterator</span>();</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 58px;"></div><div class="CodeMirror-gutters" style="height: 58px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre><hr /><p> </p><h3 id='linkedlist'><strong><span>LinkedList</span></strong></h3><ol start='' ><li><p><span>迭代问题可以用 foreach</span></p></li></ol><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>4</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"访问链表元素:"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span>(<span class="cm-variable-3">String</span> <span class="cm-variable">animal</span>: <span class="cm-variable">animals</span>) {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">print</span>(<span class="cm-variable">animal</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">print</span>(<span class="cm-string">", "</span>);</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 115px;"></div><div class="CodeMirror-gutters" style="height: 115px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre><p><span>2.</span><strong><span>使用for循环</span></strong></p><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>5</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"访问链表元素:"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span>(<span class="cm-variable-3">int</span> <span class="cm-variable">i</span><span class="cm-operator">=</span><span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator"><</span> <span class="cm-variable">animals</span>.<span class="cm-variable">size</span>(); <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">print</span>(<span class="cm-variable">animals</span>.<span class="cm-variable">get</span>(<span class="cm-variable">i</span>));</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">print</span>(<span class="cm-string">", "</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 144px;"></div><div class="CodeMirror-gutters" style="height: 144px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre><ol start='3' ><li><p><strong><span>使用iterator()方法</span></strong></p></li></ol><pre class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" spellcheck="false" lang="java"><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 12.3984px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 30px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>5</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -30px; width: 30px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"LinkedList使用iterator()方法:"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Iterator</span><span class="cm-operator"><</span><span class="cm-variable-3">String</span><span class="cm-operator">></span> <span class="cm-variable">iterate</span> <span class="cm-operator">=</span> <span class="cm-variable">animals</span>.<span class="cm-variable">iterator</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">while</span>(<span class="cm-variable">iterate</span>.<span class="cm-variable">hasNext</span>()) {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 21px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">print</span>(<span class="cm-variable">iterate</span>.<span class="cm-variable">next</span>());</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -30px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 21px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">print</span>(<span class="cm-string">", "</span>);</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 144px;"></div><div class="CodeMirror-gutters" style="height: 144px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 29px;"></div></div></div></div></pre><p><span>LinkedList和ArrayList都实现Collections框架的List接口。 但是，它们之间存在一些差异。</span></p><figure><table><thead><tr><th style='text-align:left;' ><span>LinkedList</span></th><th style='text-align:left;' ><span>ArrayList</span></th></tr></thead><tbody><tr><td style='text-align:left;' ><span>在单个位置存储3个值（上一个地址，数据和下一个地址）</span></td><td style='text-align:left;' ><span>将单个值存储在单个位置</span></td></tr><tr><td style='text-align:left;' ><span>提供list的双链接列表实现</span></td><td style='text-align:left;' ><span>提供可调整大小的数组实现</span></td></tr><tr><td style='text-align:left;' ><span>每当添加元素时，上一个和下一个地址都会更改</span></td><td style='text-align:left;' ><span>每当添加元素时，该位置之后的所有元素都会移动</span></td></tr><tr><td style='text-align:left;' ><span>要访问元素，我们需要从头开始迭代到元素</span></td><td style='text-align:left;' ><span>可以使用索引随机访问元素。</span></td></tr></tbody></table></figure><hr /><p> </p><h3 id='优先队列priorityqueue'><span>优先队列PriorityQueue</span></h3><p><code>PriorityQueue</code><span> 是 Java 中的一种数据结构，它实现了 </span><code>Queue</code><span> 接口。它是一个基于优先级的队列，其中元素按照它们的自然顺序或者根据传递给构造函数的比较器进行排序。</span></p><p><span>在这段代码中，</span><code>PriorityQueue</code><span> 被用来实现一个最小堆。构造函数接受两个参数：初始容量 </span><code>k</code><span> 和一个比较器 </span><code>Comparator.comparingInt(a -> a)</code><span>。这个比较器用来确定元素的顺序，它表示元素按照它们的自然顺序进行排序。</span></p><p><code>Comparator.comparingInt(a -> a)</code><span> 是一个比较器，它用来确定元素的顺序。它是 </span><code>Comparator</code><span> 类的一个静态方法，接受一个函数作为参数。这个函数用来从元素中提取一个 </span><code>int</code><span> 值，然后根据这个值对元素进行排序。</span></p><p><span>在这段代码中，传递给 </span><code>comparingInt</code><span> 的函数是 </span><code>a -> a</code><span>，它是一个恒等函数，表示元素本身就是要比较的值。因此，这个比较器表示元素按照它们的自然顺序进行排序。</span></p><blockquote><p><span>同时由于 这类采用Integer的类型的，引入了泛型。Integer是java的一个类，是整数类型的对象，是Int类型的包装类，基本数据int和Integer是不同的，</span><strong><font color='orange'><span>基本数据类型存储在栈中，而引用类型存储在堆中</span></font></strong><span>，队列这种类，只能存储引用类型的元素。</span></p></blockquote><hr /><p> </p><h3 id='关于拆箱和装箱'><strong><span>关于拆箱和装箱</span></strong></h3><p> </p><blockquote><p><code>Integer</code><span> 类型的对象可以直接与 </span><code>int</code><span> 类型的值进行比较。这是因为 Java 支持自动装箱和拆箱。</span></p><p><span>自动装箱是指将基本数据类型的值自动转换为对应的包装类对象。例如，当你将一个 </span><code>int</code><span> 类型的值赋给一个 </span><code>Integer</code><span> 类型的变量时，Java 会自动将这个 </span><code>int</code><span> 值转换为一个 </span><code>Integer</code><span> 对象。</span></p><p><span>自动拆箱是指将包装类对象自动转换为对应的基本数据类型的值。例如，当你将一个 </span><code>Integer</code><span> 对象与一个 </span><code>int</code><span> 值进行比较时，Java 会自动将这个 </span><code>Integer</code><span> 对象转换为一个 </span><code>int</code><span> 值。</span></p><p><span>因此，在这段代码中，当 </span><code>Integer</code><span> 类型的堆顶元素与 </span><code>int</code><span> 类型的数组元素进行比较时，Java 会自动将堆顶元素拆箱为一个 </span><code>int</code><span> 值，然后再进行比较。</span></p></blockquote></div></div>
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