How to make a toggle panel?

Question

Java

Hello.
I am programming a graphical calculator, I want to make a panel at the top The

question is that I don’t know how to make the buttons appear and disappear, that is, I don’t know how to program this panel at all.
Sort of like this
When normal

When engineering

Answer 1

There is one tutorial here .
But it seems to me that if you want to make a really good calculator, then it's better to make it based on reverse polish notation so that you can read complex expressions like:

1 + 2*3
(2 - 4) / 5
9/2 - 3/4