Last time, we said a type is a set of values. A box can only
hold one value from the set. We can change this value and write
a new value from the set. We're not allowed to use values
that are not in the set.
Here are some of the more important types in Java: int,
double, and char.
These three types fall into a category of types called
primitive types. We'll explain why they're called primitive
types once we introduce object types.