Strange NullPointerException in String Array Issue

Question

Can anyone help me on this issue?

   'public class DataBase {
        static Article[] arts;
        public static int FileNumber;
        public static String[] FileList;
        static File root;

        public DataBase(String ID, String TA) 
        {
            File root=new File(pth);
            FileList=root.list().length;
            String[] FileList=new String[FileNumber];
            for(int i=0;i<FileNumber;i++)
            {
                 FileList[i]=new String(root.list()[i]);
            }
            arts=new Article[FileNumber];
        }

        public void phase_0()   //Initializare lista articole
        {
            for(int i=0;i<FileNumber;i++)
            {
                 System.out.println(FileList[i]); ******
            }
        }
    }'

I get runtime error at the line marked with **. I don't have any idea about the issue. Can somebody help?

To be clarified, in static void main i first use constructor

DataBase db=new DataBase(...)

and then

db.phase_0();

and i get at the error on this last method at the specified line. Thanx in advance! The PATH is inserted when necessary, I assure that is NOT the problem

What have you tried when debugging? Is listaFisiere null when the exception is thrown? If so, where can it be set except in the constructor? — ekholm
– ekholm, Commented Jun 21, 2012 at 9:17
I don't really know the issue. I've verified and FileList (i've changed all names to english) seems to be null at that point.. But I don't understand why. I thought I've initialized the string correctly. I'm stuck on this idiotic issue for a couple of days — TudorV
– TudorV, Commented Jun 21, 2012 at 15:22
As per conventions, public static int FileNumber; should be public static int FILE_NUMBER; — zengr
– zengr, Commented Jun 21, 2012 at 21:23
@zengr That convention I believe only applies to constant values: source — NominSim
– NominSim, Commented Jun 21, 2012 at 21:28
My bad, yes you are right, it should be public static int fileNumber; — zengr
– zengr, Commented Jun 21, 2012 at 21:32

Alexander · Accepted Answer · 2012-06-21 21:20:30Z

3

You are shading your public static String[] FileList with this line:

String[] FileList=new String[FileNumber];

It should be:

FileList = new String[FileNumber];

answered Jun 21, 2012 at 21:20

Alexander

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NominSim · Accepted Answer · 2012-06-21 21:25:18Z

1

Your global FileList array gets overridden by the local array in your constructor. Remove the String[] from the local declaration to make it global.

answered Jun 21, 2012 at 21:25

NominSim

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