Accessing Static variables

Question

public class Bicycle {

    private int cadence;
    private int gear;
    private int speed;
    private int id;
    private static int numberOfBicycles = 0;

    public Bicycle(int startCadence, int startSpeed, int startGear){
        gear = startGear;
        cadence = startCadence;
        speed = startSpeed;

        id = ++numberOfBicycles;
    }
       // ...
}

I learned in my class that Static variables should be accessed by calling with class name. i.e. ClassName.VariableName

But in the code above, how is this statement id = ++numberOfBicycles; compiled without errors, even though the variable numberOfBicycles is static

Answer 1

Static variables are owned by class rather than by its individual instances (objects). Referring static variables outside the class is by ClassName.myStaticVariable but inside the class it is similar to other instance variables.

You can always use static variables in non-static methods but you cannot use non-static variables in static methods reason being when static methods are loaded other non-static instance variables are not created.

So your statement id = ++numberOfBicycles; is perfectly valid and will compile without errors.

Answer 2

Static variables are the shared variables. So you can access them using either the Classname.staticVariable or using an object of the class instance.staticVariable. In any case you will be referring to the single copy of the variable in memory, no matter how many objects you create.