Unable to use instance variable in a static method

Question

Why we cannot use instance variable in a static method? I know that static methods are called without creating instance of classes but what restricts the non static variable to be used in static method?

class MyClass
{
    // non-static instance member variable
    private int a;
    //static member variable
    private static int b;

    //static method
    public static void DoSomething()
    {
        //this will result in compilation error as “a” has no memory
        a = a + 1;
        //this works fine since “b” is static
        b = b + 1;
    }
}

You need an instance of your class in order to access an Instance Field. static fields are accessible by instance and static methods, but not the other way around. — Philippe Paré
– Philippe Paré, Commented Sep 14, 2015 at 19:38
possible duplicate of Why static classes cannot have nonstatic methods and variables — Ehsan Sajjad
– Ehsan Sajjad, Commented Sep 14, 2015 at 19:39
Since there is an a in each instance, which would you expect to be incremented? What if you haven't created any instances yet? You could pass an instance to a static method as a parameter. — HABO
– HABO, Commented Sep 14, 2015 at 19:40
To @HABO's point: are you expecting to instantiate only one object of type MyClass? If so, consider the infinitely abusable Singleton Pattern instead of creating a static class. — Bob Kaufman
– Bob Kaufman, Commented Sep 14, 2015 at 19:50

Salah Akbari · Accepted Answer · 2015-09-14 20:36:20Z

6

Trying to put a non-static variable inside a static method makes the compiler wonder which instance of this variable should I really be updating? The static methods are not related to a class instance, so it will be impossible to call an instance variable on an instance when no instance exists.

edited Sep 14, 2015 at 20:36

answered Sep 14, 2015 at 19:39

Salah Akbari

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