Hui-s-notebook/logseq-java/journals/2022_04_14.md at 0e31c0d985c41fefa41a0bddeccbdc77148aad8e - Hui-s-notebook - Gitea: Git with a cup of tea

lostecho/Hui-s-notebook

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Lostecho c7947017c3 add logseq-java

2024-02-02 00:12:49 +08:00

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StringBuilder
StringBuffer
Arrays
System
Runtime
Math
Random
UUID
BigDecimal
总结 collapsed:: true
- StringBuilder
  - 长度，内容可变的字符串
  - 常用API
    - append
    - insert
    - capacity
    - length
    - setCharAt
    - deleteCharAt
    - delete
    - reverse
    - substring
    - indexOf
    - lastIndexOf
- StringBuffer
  - 所有API及操作与StringBuilder一致
- Arrays
  - toString
  - sort
  - binarySearch
  - copyOf
  - equals
- System
  - exit
  - gc
  - currentTimeMillis
  - nanoTime
  - arraycopy
  - getProperties
  - Runtime
- Math
  - random
  - abs
  - pow
  - max
  - min
  - round
- Random
  - ```
  Random a = new Random();
```
- 回溯历史
  - Random(long seed)
- {{embed UUID}}
- BigDecimal
  - 解决浮点数精度丢失的问题
  - 使用字符串作为参数最精准
  - 加减乘除
    - add
    - subtract
    - multiply
    - divide
  - 除法除不尽
    - 收尾
      - ROUND_DOWN 去尾
        
        只保留小数点后指定位数
      - ROUND_UP 收尾
        
        保留小数点后指定位数,如果保留位的后一位不为零,保留位的值加1
      - ROUND_HALF_UP 四舍五入
        
        保留小数点后指定位数,如果保留位的后一位<5,保留位数的值不加1,保留位的后一位>=5,保留位数的值加1