anonymous inner class

[prateek narang]

hi group,
in the filter() method of the code below the argument passed is final, this argument is used in the anonymous class written inside that method. My question is that why we have to declare this argument as final?

import java.io.*;
import java.util.*;
public class DirList2 {
  public static FilenameFilter 
  filter([B]final String afn[/B]) {
    // Creation of anonymous inner class:
    return new FilenameFilter() {
      String fn = afn;
      public boolean accept(File dir, String n) {
        // Strip path information:
        String f = new File(n).getName();
        return f.indexOf(fn) != -1;
      }
    }; // End of anonymous inner class
  }
  public static void main(String[] args) {
    File path = new File(".");
    String[] list;
    if(args.length == 0)
      list = path.list();
    else 
      list = path.list(filter(args[0]));
    for(int i = 0; i < list.length; i++)
      System.out.println(list[i]);
  }
} 

regds..
--prateek--

[Manfred Leonhardt]

Hi Prateek,
Quite simply, because the class will out live the method. Therefore, if it was not final the reference to it would be gone and the anonymous class would be using a undefined reference variable. Not very good for a stable environment.
Regards,
Manfred.

[prateek narang]

But Manfred this means that final object lives after the scope of the method has been finished. I'm not sure about the scope of the final variables. can anybody explain a bit about it.