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<p>首先增强for循环和iterator遍历的效果是一样的，也就说增强for循环的内部也就是调用iteratoer实现的，但是增强for循环有些缺点，例如不能在增强循环里动态的删除集合内容。不能获取下标等。</p>
<h4><a id="_2"></a>结论:</h4>
<p>如果是ArrayList，用三种方式遍历的速度是for>Iterator>foreach，速度级别基本一致；<br>
如果是LinkedList，则三种方式遍历的差距很大了,数据量大时越明显(一般是超过100000级别)，用for遍历的效率远远落后于foreach和Iterator，Iterator>foreach>>>for；</p>
<h4><a id="_7"></a>过程：</h4>
<p>模拟100000条数据，放入ArrayList和LinkedList，对两个List分别用三种方式进行遍历，耗时如下图所示：</p>
<pre class="blockcode"><code class="prism language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Test</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">// 初始化</span>
List<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> arrList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
List<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> linkList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LinkedList</span><span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token number">100000</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
arrList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span> String<span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span> i <span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span>
linkList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span> String<span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span> i <span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> <span class="token string">"---------------------测试结果------------------------"</span> <span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> <span class="token string">"for arrList 时间是 \t"</span> <span class="token operator">+</span> <span class="token function">testFor</span><span class="token punctuation">(</span> arrList <span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> <span class="token string">"iterator arrList 时间是 \t"</span> <span class="token operator">+</span> <span class="token function">testIterator</span><span class="token punctuation">(</span> arrList <span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span>
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