Two Buttons in a Frame
Let's develop a new program:
- A frame will hold two buttons, one labeled "Red" and the other "Green."
 
- The FlowLayout layout manager will be used so the buttons will be
    nicely positioned in the frame.
 
- When the button marked "Red" is clicked, the background will turn red.
  
- When the button marked "Green" is clicked, the background will turn green.
 
- There will be an event listener that  listens  to the clicks
    from both buttons.
  
- When the "close button" of the frame is clicked, the application will quit.
 
- There will be a listener for  window events.
  
This is very close to a previous example program.
It would be sensible to copy that file and edit it for the new application.
However,
as a review of these somewhat confusing GUI implementation details,
let us start from scratch.