Java How to Program (early objects), 9/e

8.11 static Class Members

Every object has its own copy of all the instance variables of the class. In certain cases, only one copy of a particular variable should be shared by all objects of a class. A static field — called a class variable —is used in such cases. A static variable represents classwide information —all objects of the class share the same piece of data. The declaration of a static variable begins with the keyword static.

Let’s motivate static data with an example. Suppose that we have a video game with Martians and other space creatures. Each Martian tends to be brave and willing to attack other space creatures when the Martian is aware that at least four other Martians are present. If fewer than five Martians are present, ...