Cannot refer to a non-final variable inside an inner class

Posted on 2004-08-20
Medium Priority
Last Modified: 2010-05-18
I have to get an object from an inner class method :

  Object  myObject ;
  GetObject(objectKey,new ResultReader () {
    public boolean Read (Collection data) {
      myObject = GetObjectFromCollection(data) ;
  ) ;

  // Now use myObject
  String s = myObject.toString() ;
  // ...

The ResultReader class is an interface, for which the Read method is called by the
'GetObject' method when it passes the object bakc to the caller :

  public interface ResultReader {
    public boolean Read(Collection data);

The problem is that such a code generates an error message at compilation :
"Cannot refer to a non-final variable 'myObject' inside an inner class defined in a different method"
at the line containing "myObject = GetObjectFromCollection(data) ;"

A way to bypass this limitation I have been using is to store the object I get into a Vector defined as 'final',
but I found the solution quite inelegant :

  Object myObject ;
  final  Vector v = new Vector() ;

  GetObject(objectKey,new ResultReader () {
    public boolean Read (Collection data) {
      Object myTempObject = GetObjectFromCollection(data) ;
      v.add(myTempObject) ;
  ) ;

  // Get the object back from the Vector
  myObject = v.get(0) ;

  // Now use myObject
  String s = myObject.toString() ;
  // ...

Do you know any other solution that would be more elegant : define the inner class in another manner? declare the object I have to retrieve in some special way?

And why is there such a limitation with the use of inner classes ?

Thanks for answers.

Question by:stsanz

Accepted Solution

Venci75 earned 1000 total points
ID: 11851884
this is not a limitation of the inner classes - but limitation of the Anonymous classes - they can access local valiables of the method which are defined as final.
possible solutions -
1. use inner - and not anonymous class
2. use a member variable of the class - instead of mthod local vatiable

Expert Comment

ID: 11853323

Expert Comment

ID: 11857540
I don't quite understand your getObject(), is this how it looks in your code? or you're trying to show how it works?

From what is written in getObject(), you are using anonymous class but still an inner class type.

Here is an example to show you that myObject can be assgned within inner class:

public interface Inner{
  public void getObject();

class InnerClass{

Object myObject;

void myToString(){
  // Anonymous class with its method call
  (new Inner(){
   public void getObject(){
     myObject = new Object();

public static void main(String[] args){
  new InnerClass().myToString();  

Is this what you're trying to do?

Expert Comment

ID: 26829780
this is incomprehensible

Featured Post

The new generation of project management tools

With monday.com’s project management tool, you can see what everyone on your team is working in a single glance. Its intuitive dashboards are customizable, so you can create systems that work for you.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Java had always been an easily readable and understandable language.  Some relatively recent changes in the language seem to be changing this pretty fast, and anyone that had not seen any Java code for the last 5 years will possibly have issues unde…
Introduction Java can be integrated with native programs using an interface called JNI(Java Native Interface). Native programs are programs which can directly run on the processor. JNI is simply a naming and calling convention so that the JVM (Java…
Video by: Michael
Viewers learn about how to reduce the potential repetitiveness of coding in main by developing methods to perform specific tasks for their program. Additionally, objects are introduced for the purpose of learning how to call methods in Java. Define …
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.
Suggested Courses

607 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question