We will understand how garbage collection works with a few simple examples. We don't want to code a garbage collection process and we won't dive too deep into all the details about this complex process. Our goal is to create object-oriented code with Java 9 and not to create a new implementation of the JVM.

Now, we will add some code to the previously created Rectangle class to make Java execute some code before the garbage collection removes an instance of this class from memory. We only add this code to have a clear understanding of how garbage collection works. It is not recommended, and usually not necessary at all, to add code to the finalize method as we will do right now. Think about the next code as a code snippet just for educational purposes and not something we should do with our classes. We must take into account that we don't know when the garbage collection process will determine that it is necessary to claim back the memory used by...