[java] Autoboxing

Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes. For example, converting an int to an Integer, a double to a Double, and so on. If the conversion goes the other way, this is called unboxing.

autoboxing 是一種 java compiler 自動轉換 primitive type 與 對應的 object wrapper class 的一種機制。像是，把 int 自動轉換到 Integer object內。 反向過來說，就是一種unboxing。

ref:

JavaSE6Tutorial/CH04.md at master · JustinSDK/JavaSE6Tutorial
https://github.com/JustinSDK/JavaSE6Tutorial/blob/master/docs/CH04.md
Autoboxing and Unboxing (The Java™ Tutorials > Learning the Java Language > Numbers and Strings)
http://docs.oracle.com/javase/tutorial/java/data/autoboxing.html