non-static variable n cannot be referenced from a static context,该如何解决_J2SE

non-static variable n cannot be referenced from a static context
class Num{
    private int i=0;
    public void add(){i++;System.out.println("i="+i);}
    public Num(){}
}
class Ber{
    private Num n;
    public Ber(Num n){
        this.n=n;
        this.n.add();
    }
}
public class Test {
    Num n=new Num();
    public static void main(String[] args){
        for(int i=0;i<3;i++){
        Ber b=new Ber(n);
        }
    }
}

红色那行出现错误：non-static variable n cannot be referenced from a static context
找不到原因啊，哪位大神帮帮忙！！！

------解决方案--------------------
静态方法中不能调用非静态成员或方法，jvm加载顺序，静态优先。
修改为:


class Num{
    private int i=0;
    public void add(){i++;System.out.println("i="+i);}
    public Num(){} 
}
class Ber{
    private Num n;
    public Ber(Num n){
        this.n=n;
        this.n.add();
    }
}
public class Test {
    
    public static void main(String[] args){   
        Num n=new Num();
        for(int i=0;i<3;i++){
        Ber b=new Ber(n);
        }
    }
}