Comparable is an interface already implemented in Java.
https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html
http://tutorials.jenkov.com/java/interfaces.html
What you need to do there is create two classes Customer (which implements Comparable) and HighEarner which inherits Customer. You also need a main class which you can name whatever(ex: Program or FlowerShop).
solved Understanding the requirement of an OOP programming [closed]