Lets See This Example.

public class Test {

    private int count=0;
    public static void main(String args[]) throws IOException {
        count++; //compiler error: non-static variable count cannot be referenced from a static context
    }
}

Static variable in Java belongs to Class and its value remains same for all instance. static variable initialized when class is loaded into JVM on the other hand instance variable has different value for each instances and they get created when instance of an object is created either by using new() operator or using reflection like Class.newInstance().

 So if you try to access a non static variable without any instance compiler will complain because those variables are not yet created and they don't have any existence until an instance is created and they are associated with any instance