I don't understand why the static method can't receive a non-static member, but it's an example.

class Number {

int n;
public Number(int n) { this.n = n; }

}

public class Example {

static void plusTen(Number x) { x.n += 10; }
public static void main(String args[]) {
    Number ob = new Number(5);
    plusTen(ob);
    System.out.println(ob.n);
}

}

It's a practice question for "Luxury Java Essential" The static method cannot be accessed as a non-static member If then, In the static void plus Ten (Number x) line, Since x.n is a non-static member, shouldn't there be a compilation error? But when I actually coded it, Here's the result. Please help me. I don't understand.