If a variable can simultaneously have different values for different instances of a class (objects), it should be an instance variable. Examples are the account number, quantity, size, or name of an object. If a variable is must always be the same at any given time for every instance of a class, it should be a static variable. Examples are final variables (constants), the object count, the next account number to be assigned, and dollar totals across all objects in a class. Two special cases: Static methods can't access instance variables. Variables in interfaces must be static and final.