https://msdn.microsoft.com/en-us/library/yz2be5wk.aspx
int i = 123;
object o = i; // boxing (값 형식 -> 참조 형식)
int j = (int) o; // unboxing (참조 형식 -> 값 형식)
https://msdn.microsoft.com/en-us/library/yz2be5wk.aspx
int i = 123;
object o = i; // boxing (값 형식 -> 참조 형식)
int j = (int) o; // unboxing (참조 형식 -> 값 형식)