要重装系统的想法一经冒出来，就挥之不去。虽已多次暗示自己重装挺麻烦的，可就是劝不住心底另一个自己，既如此那就动手把 Mac 归置归置一下吧。

IKEv2, or Internet Key Exchange v2, is a protocol that allows for direct IPSec tunneling between the server and client. In IKEv2 implementations, IPSec provides encryption for the network traffic. IKEv2 is natively supported on some platforms (OS X 10.11+, iOS 9.1+, and Windows 10) with no additional applications necessary, and it handles client hiccups quite smoothly.

A simple Java program to print out a calendar for the current month, and highlight the current day.

Relations among different classes might be clear for me, however, the way using unified modeling language (UML) to represent it is something new to me. A note on this topic is worth taking to make it on my dictionary. Taken from Core Java Volume I (11th edition) - Cay S. Horstmann.

A simple command to download youtube videos with best video and audio quality.