Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed character class near index 0 [ ^
Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed character class near index 0 [ ^
出现此错误应该是字符转义出现问题：
System.out.println(str.replaceAll("[", "22"));
解决方案：在[之前加上\\
System.out.println(str.replaceAll("\\[", "22"));
文章来自：http://www.cnblogs.com/wangchaoyuan/p/5965460.html