Java 8 後新觀念理解順序:
1.Type Inference:
    https://docs.oracle.com/javase/tutorial/java/generics/genTypeInference.html

2.Local variable type inference:
    https://codertw.com/%E4%BC%BA%E6%9C%8D%E5%99%A8/145426/

3.Generic Types:
   https://docs.oracle.com/javase/tutorial/java/generics/why.html