Processing, Arduino, Raspberry Pi.
I've assembled these few notes for anyone starting to use Processing and Java. I'm a new user of Google Sites, some things are not as I'd like and only the first few items are here.
These first few exercises could take just a few minutes each, and after them you'll begin to understand Processing and Java. (You might get distracted trying things and take longer.)
Processing
Install Processing. (Download, Install, Run Processing.)
Processing Basic Shapes. Start with some simple shapes and colours.
Processing Help Help for every keyword.
Processing Setup and Draw. Draw a shape wherever the mouse is.
Circle_Collision. Use an existing example, and improve it.
Cartoon Automation. Add image(s) to an animation.
Processing Dark Theme notes. Change the IDE to dark theme.
Conditional Control Use conditional logic to select colours.
There are lots of other things to try and directions to go. You could try all the examples, you could look at the help and try lots of things there. In the examples there's "Serial" and you can make Processing and Arduino talk to each other. There are examples that load data from the internet, and others that talk between Processing programs. You can switch mode to Javascript learn that, and make a dynamic web-site. You can switch mode to Android and put a program on your phone.
Arduino Get Started with Arduino (First few simple programs.)
Nano Arduino Nano (Clone) Repair Make Nano Clone Usable
ESP8266 ESP8266 Fan Control (ESP8266 Controlling a Fan.)