要调用内部类的函数，我只需要内部类的一个对象。但是如果我已经创建了对象，为什么我不能在任何我想要的地方调用内部类的方法呢？错误试图暗示什么？

class Outer 
{
    int x;

    class Inner // creating an Inner class
    {
        public void display()
        {
            System.out.println("Hello from Inner class"+x);
        }
    }

    Inner i = new Inner();
    i.display(); // This is where the error comes. Why do I have to create a method to call
                 // methods of my inner class. Why Can't I call it anywhere I want?
}

public class Main
{
    public static void main(String[] args) 
    {
        System.out.println("Hello World");
    }
}