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Do you know what "private" and "static" mean?
"private" is an
access specifier. It tells you that the member is only visible inside the class - other classes can't access the private members of a class.
"static" means that the variable is a class-level variable; there's only one variable, which is shared by all instances of the class. See
Understanding Instance and Class Members for more info.
So, if you combine these for a member variable, you get a member variable that's only visible inside the class, and of which there's only 1 copy, shared by all instances of the class.
Private static member variables are useful for a number of constructions, for example to implement the Singleton design
pattern in
Java. Here's an example: