So far, the programs we've seen have done their entire computation inside a
single expression in the println call. For more complicated
programs, we need to be able to declare and use variables. So far, we have
only used simple integers. To declare a variable called n to hold
an integer, we can write:
int n;
This is a declaration which tells Java to reserve some space, and
says that we are going to call it n from now on. The type
int means that the variable is an integer, i.e. it can only hold
whole numbers. A couple of variations are worth mentioning. We can write:
int height, width, depth;
to declare several variables of the same type at once. Also, we can write:
int count = 10;
to declare a variable, and give it an initial value at the same time.
You may think it verbose to use long variable names like count
rather than just c. However, in larger programs, there are
typically hundreds or thousands of variables. If someone is going to be able
to read and maintain a program without getting confused, especially if it is
not the original author or it has been a long time since the code was written,
the variables must have meaningful names. Single-letter names are only used
for temporary working variables such as indexes which have no particular
significance.