首先说 空 这件事，空 ：One of the most common pitfalls in many programming languages, including Java is that of accessing a member of a nullreferences, resulting in null reference exceptions. In Java this would
一、常量与变量（var、val、const的使用与区别）===============================================================================================1.var、val、const的使用与区别var 称为可读写变量 如下和java对比所示：//java
int a = 2;
a = 3;
//kotli
