With the buttons now laying out correctly, it was fairly trivial to add a JTextField at the top of the frame to serve as the calculator's display. To prevent overflows, I've decided to limit the display to 8 characters. Time to implement this.

Yes, this is probably overkill for simply setting the text on a JTextField. However, I wanted the ability to display text to the screen for errors, such as overflow or undefined. This method allows for me to do that, while having it conveniently abstracted away.

With the UI done, now it's time to make it so the calculator can actually, you know, calculate. This meant it was time for logic and flow control. To accomplish this, I decided to create two enums, one to store the state of the calculator, and the other to keep track of the operation the user has selected.

Now it's time to get input from the keypad. In my experience, UI code tends to be rather verbose. Java code also tends to be rather verbose. Java UI code is exactly as you'd expect. When it came to getting input from the keypad, I found it easier to treat the input as a string which we will cast to an integer later, as this allows each button to simply append it's corresponding number to the string. When the equals button is pressed, we then use this simple method, typecasting the return to an integer in order to round, because this is intended to be an integer calculator:

All that's left is to pass the the return into the setDisplay() method we made earlier, and we're done!

Overall, this was a fairly straightforward project. I didn't even need to Google anything really, I was able to simply work for the Swing documentation. My goal here was to have a bit of a challenge and gain a better understanding of UI programming. Mission accomplished.