SimpleDateFormat简介
格式化时间工具类，可格式化年月日等自定义时间格式。
SimpleDateFormat构参
- SimpleDateFormat()
- SimpleDateFormat(String pattern)
- SimpleDateFormat(String pattern, Locale locale)
- SimpleDateFormat(String pattern, DateFormatSymbols formatSymbols)
一般使用一个String参数的构参，传入参数一般为时间的格式化格式，其中包括格式如下表：
| 符号 | 含义 | 介绍 | 例 |
|---|---|---|---|
| G | era designator | Text | AD |
| y | year | Number | 2009 |
| M | month in year | Text & Number | July & 07 |
| d | day in month | Number | 10 |
| h | hour in am/pm (1-12) | Number | 12 |
| H | hour in day (0-23) | Number | 0 |
| m | minute in hour | Number | 30 |
| s | second in minute | Number | 55 |
| S | millisecond | Number | 978 |
| E | day in week | Text | Tuesday |
| D | day in year | Number | 189 |
| F | day of week in month | Number | 2 (2nd Wed in July) |
| w | week in year | Number | 27 |
| W | week in month | Number | 2 |
| a | am/pm marker | Text | PM |
| k | hour in day (1-24) | Number | 24 |
| K | hour in am/pm (0-11) | Number | 0 |
| z | time zone | Text | Pacific Standard Time |
| ’ | escape for text | Delimiter | (none) |
| ’ | single quote | Literal | ’ |
例如：SimpleDateFormat("yyyy.MM.dd G 'at' hh:mm:ss z") 输出文本：2019.01.14 公元 at 10:15:53 CST
更多时间相关内容，可看菜鸟教程：飞机票