Exercise 4

1. Design the above frame

2. The number is initialized with the constructor of the frame to the first number in the

   combo box.

3. Each time the combo box changes selection, the number changes to its current selection.

4. The text area is updated each time one of the two buttons is pressed. If the button

   Increment is pressed, the number is incremented and appended to the text area. If the button Decrement is pressed, the number is decremented and appended to the text area.