error with inner class object

import java.io.*;
class YY
{

   int a=0;
   void putValue(int m)
   {
        a=m;
    inner x=new inner();
        x.display();
   }
   class inner
   {
    void display()
        {
       System.out.println("value of a:"+a);
        }
   }
}

class InnerYY
{
   public static void main(String args[])
   {
    YY ob=new YY();
    ob.putValue(90);
    YY.inner i = new YY.inner();
    i.display();
   }
}

while running this program i'm getting the following error...

InnerYY.java:27开发者_运维技巧: an enclosing instance that contains YY.inner is required YY.inner i = new YY.inner(); ^ 1 error

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Your Inner class is non-static, so you havee to instantiate it with an instance of YY.

In your case that is Inner inner = ob.new Inner();

Note that:

• If you want that class public, you can refer to it as YY.Inner (but you can't instantiate it that way)

• by convention you must use capitalized class names (Inner rather than inner). That said, I think it's worth mentioning that usually in Java (but that's not as imperative as the capitalized class name) the opening curly bracket stays on the same line.

---

To reference YY, InnerYY would have to actually be inside YY (moved before the closing break). However you then couldn't have a static main function, which appears to be what it's for.

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You try to create non-static inner class from static call YY.inner(). So you need to create object yy = new YY() and then call inner = new yy.inner(). Or to make inner class static.