You have good practice for coding in response already done.

I would point out concept concern.

If you use Java, do not use ksh or c-shell procedural paradigme.

Because of ATM constraint, all your constant values (like 20, 40, 60, 100) have to be in an Interface and never hard coded in an other place. [in a normal environment they can be put in aFile.properties]

Use an Enum for binding 1 and 20, 2 and 40 and so on

So you can print for all Enum.values(), and always avec the choice in front of the value

Read, and try samples from Effective Java, this book is inevitable, with another one to understand Pattern Design (Of all those that I was able to read this is one who gave me the click, to understand the functioning of the design pattern) : Head first Design Pattern

It begins with Observer pattern. With it, you have to remove switch and other if revealing a way to think the solution for the future, and not transmit the problem to the objects build to solve them.

Another point : search in Effective Java StringBuilder

With those two books you will avoid all beginner mistakes, and raise rapidly Java professionnal status.

You have good practice for coding in response already done.

I would point out concept concern.

If you use Java, do not use ksh or c-shell procedural paradigme.

Because of ATM constraint, all your constant values (like 20, 40, 60, 100) have to be in an Interface and never hard coded in an other place. [in a normal environment they can be put in aFile.properties]

Use an Enum for binding 1 and 20, 2 and 40 and so on

So you can print for all Enum.values(), and always with the good choice in front of the value

Read, and try samples from Effective Java, this book is inevitable, with another one to understand Pattern Design (Of all those that I was able to read, this is one who gave me the click, to understand the functioning of the design pattern) : Head first Design Pattern

It begins with Observer pattern. With it, you have to remove switch and other if revealing a way to think the solution for the future, and not transmit the problem to the objects build to solve them.

Another point : search in Effective Java StringBuilder

With those two books you will avoid all beginner mistakes, and raise rapidly Java professionnal status.