how can i do a design patterns to my code?
the code made by java to design cash register.
design patterns are known design solutions to recurring problems, the idea is that lots of applications can be broken down to similar problems and it is your ability to identify sections of your code that can benefit from using these known patterns.
Patterns can help in the development, but are not a solution in themselves, without more knowledge of your cash register program it would be difficult to know which if any patterns could be used.
I recommend that you read the book on design patterns.