RxJava 复刻简版之二，调用流程分析之案例实现

接上篇：https://blog.csdn.net/da_ma_dai/article/details/131878516
代码节点：https://gitee.com/bobidali/lite-rx-java/commit/05199792ce75a80147c822336b46837f09229e46

java 类型转换 kt

类型：

Any == Object

泛型：

协变: out T == ? extends T
逆变: in T  == ? super T