# in the process of learning

Reference:

## etc

1. two types of array declaration: `dataType[] arrayRefVar;` and `dataType arrayRefVar;`. The former is preferred, while the latter is for the convenience of C++ programmers.

2. `length` `length()` `size()`. `length`属性针对数组，`length()`针对字符串string，`size()`针对泛型集合。

3. `List lt;` 会报错 `List lt = new ArrayList();` 则不会报错。自定义对象如果不初始化，再访问时报错`java.lang.NullPointerException`。

4. 用`==`比较字符串实质是比较地址，永远不相等，应该使用`equals()`方法。

## data structure

### arraylist

<https://blog.csdn.net/GongchuangSu/article/details/51514389>