In computer science's object-oriented programming, class variables (static fields) contain information which is associated with all instances of a class. If all tanks have one cannon, then it is not necessary to specify, in an instance variable for each tank object, that each tank has only one cannon; rather, one can simply define a class variable which does this and thus all instances of the class will share the variable.
... there are 92.0 males.
The median income for a household in the town is $69,819, and the median income for a family is $80,952. Males have a median income of $53,125 ...