We can think of a variable as a labeled storage box. They are also like a programmer's window to the memory of the Android device, or whatever device we are programming. Variables can store data in memory (the storage box), ready to be recalled or altered when necessary by using the appropriate label.

Computer memory has a highly complex system of addressing that we, fortunately, do not need to interact with in Java. Java variables allow us to make up convenient names for all the data that we want our program to work with; the JVM will handle all the technicalities that interact with the operating system, which in turn, probably through several layers of buck passing, will interact with the hardware.

So we can think of our Android device's memory as a huge warehouse. When we assign names to our variables, they are stored in the warehouse, ready when we need them. When we use our variable's name, the device knows exactly what we are referring to. We...