What is Invoking static methods
If a method or field is declared static, you access it through using the class name rather than a reference to a particular example of the class. Thus instead of writing
Car c = new Car("New York", 89.7);
double maximumLegalSpeed = c.getSpeedLimit();
you just write
double maximumLegalSpeed = Car.getSpeedLimit();
There does not even have to be an example of a class in order to invoke a static method within the class.
Static methods might not call non-static methods or members of the same class directly. Rather they must specify that instance of the class they are referring to. Trying to call a non-static method or member is a very general compile time error. The specific error message generated through the javac compiler will look something such as this
Error: Can't make static reference to method void floorIt() in class Car.
Of course the names and signature will be changed to match the exact method and class.