> For the complete documentation index, see [llms.txt](https://moluo.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://moluo.gitbook.io/notes/bian-cheng-xue-xi/java/java-gao-bing-fa/6.5-xian-cheng-bu-an-quan-de-lei-yu-xie-fa.md).

# 6.5线程不安全的类与写法

常见的线程不安全类与写法

* StringBuilder→StringBuffer

  StringBuilder线程不安全

  StringBuffer线程安全
* SimpleDateFormat→JodaTime

  SimpleDateFormat线程不安全

  JodaTime线程安全
* ArrayList、HashSet、HashMap等Collections

  ArrayList、HashSet、HashMap线程不安全
* 先检查再执行：if(condition(a)){handle(a);}

  不安全

请自行设计类，验证线程安全性