useful_link.md

java CAS:
http://zl198751.iteye.com/blog/1848575

java OOP:
http://baozitraining.org/blog/Java-interview-encapsulation-enheritance-polymorphism/

distributed system intro:
http://book.mixu.net/distsys/

distributed interview:
https://juejin.im/entry/5aac6ae55188252c321970e5