为什么阿里巴巴建议集合初始化时,指定集合容量大小-HollisChuang's Blog



为什么阿里巴巴建议集合初始化时,指定集合容量大小-HollisChuang's Blog

集合是Java开发日常开发中经常会使用到的。在之前的一些文章中,我们介绍过一些关于使用集合类应该注意的事项,如《为什么阿里巴巴禁止在 foreach 循环里进行元素的 remove/add 操作》。

关于集合类,《阿里巴巴Java开发手册》中其实还有另外一个规定:

本文就来分析一下为什么会有如此建议?如果一定要设置初始容量的话,设置多少比较合适?

为什么要设置HashMap的初始化容量

我们先来写一段代码在JDK 1.7 (jdk1.7.0_79)下面来分别测试下,在不指定初始化容量和指定初始化容量的情况下性能情况如何。(jdk 8 结果会有所不同,我会在后面的文章中分析)


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