Final variables
http://beginnersbook.com/2014/07/final-keyword-java-final-variable-method-class/

Using java interface
http://beginnersbook.com/2013/05/java-interface/

Difference Between Abstract Class and Interface in Java
http://beginnersbook.com/2013/05/abstract-class-vs-interface-in-java/

abstract class 就可以開 abstract method, 一定要填晒，但 extend abstract 再 extend 就要全部填晒
implements 就可以俾 coder 有得揀用邊種 property