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.
... The per capita income for the town is $35,509. 7.9% of the population and 6.8% of families are below the poverty line. Out of the total people living in poverty, 12.3% ...