Question

i’m currently just fooling around with different classes to test how they work together, but im getting an error message in NetBeans that i cant solve. Here’s my code:

class first_class.java

public class first_class {

private second_class state;

int test_tal=2;

public void test (int n) {
    if (n>2) {
        System.out.println("HELLO");
    }
    else {
        System.out.println("GOODBYE");
    }
}

public static void main(String[] args) {
    state.john();
    TestingFunStuff.test(2);

}
}

class second_class

public class second_class {

first_class state; 

public int john () {
    if (state.test_tal==2) {
        return 4;
    }
    else {
        return 5;
    }
}
}

Apparently i can’t run the method “john” in my main class, because “non static variable state cannot be referenced from a static context” and the method “test” because “non static method test(int) cannot be referenced from a static context”.

What does this mean exactly?

Screenshot of the error shown in netbeans: http://imageshack.us/photo/my-images/26/funstufffirstclassnetbe.png/

Answer 1

It means state must be declared as a static member if you’re going to use it from a static method, or you need an instance of first_class from which you can access a non-static member. In the latter case, you’ll need to provide a getter method (or make it public, but ew).

Also, you don’t instantiate an instance of second_class, so after it compiles, you’ll get a NullPointerException: static or not, there needs to be an instance to access an instance method.

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I might recommend following Java naming conventions, use camelCase instead of under_scores, and start class names with upper-case letters.