Accessing primitives in anonymous inner class

[Santiago Bravo]

Hi All,

Code example is from K&B but which shows how to create an anonymous inner class. BUT I am curious as to how a primitive can be accessed in the anonymous inner class:


****************************************
class Popcorn {

public int x = 2; // Line 1

public void pop() {

System.out.println("popcorn");

}

}
class Food {

Popcorn p = new Popcorn() { // Line 2

x=9; // Line 3 - compiler error!

public void pop() {
System.out.println("anonymous popcorn");
}
};

}
****************************************

Line 2 creates the anonymous subclass which according to polymorphism should have access to public members of the superclass.

Why doesnt the above code compile? What am I doing wrong?


thanks

[Rekha Srinath]

The x=9 is in your anonymous inner class is like an instance variable, and in general, for an instance variable, you should mention the type.

Take a normal example as this:

class Parent {
     int x = 10;
}
class Child extends Parent {
     x = 9;
}

Even in this code, you will get the same compiler error. So, you have to DECLARE the variable as an instance variable. But, you can access the inherited variable in any of the child methods in the normal way. For eg, in your Popcorn example, you can have like this:

System.out.println("anonymous popcorn" + x); // x will be 2 here, inherited from the parent Popcorn

[Campbell Ritchie]

But putting fields in a subclass which have the same name as a superclass field will "hide" the superclass field.

This can lead to all sorts of confusion later on.

[Santiago Bravo]

yes, if I had declared int x = 9; on line 3 then this is a totally new variable for the instance.

I can access variable x from the Popcorn class if I use it in a method in the anonymous inner class

[Henry Wong]

Originally posted by Santiago Bravo:
yes, if I had declared int x = 9; on line 3 then this is a totally new variable for the instance.

I can access variable x from the Popcorn class if I use it in a method in the anonymous inner class

Not sure what you are asking. Are you trying to assign the variable, without declaring a new one? If you are, then it is a statement, not a declaration. And statements are not allowed outside of an initializer, constructor, or method.

Henry

[Ankit Garg]

yes henry is absolutely right. The statement x = 9; is not allowed inside class outside any method or initializer. change the code to

class Food
{
   Popcorn p = new Popcorn()
   { 
      {
         x=9;
      }
      public void pop()
      {
         System.out.println("anonymous popcorn");
      }
   };
}

[Jesper de Jong]

Please use code tags when you post code.
[ November 09, 2008: Message edited by: Jesper Young ]