add to list with id, makes list upside down

[rompelstilchen]

hello,

I saved the content of an ArrayList<SomeClass> to a file
I write each serialised object to the file by adding to each an id that is created with list.indexOf(object) (and saved before each object)
so I can repopulated the list with SomeClass objects in the same order as they were

and once I reload the file, I do list.add(id,object)

well my list is populated upside down, I mean the first object is the last and the other way around

If i remove the id when I do the add(object), I dont have this problem

by curiosity, I wanted to know why, it does not make any sens to me so far

thanks

[Norm]

What are the values of id that are used to load the ArrayList?

[JosAH]

Can you show us some of the (relevant) code?

kind regards,

Jos

[rompelstilchen]

here you go, I stripped out all objectdata save/load, left only the id part

 public void Save(String fileName)
    {
        DataOutputStream dos=null;
        FileOutputStream fos=null;
        try 
        {
            fos = new FileOutputStream(fileName);
            dos = new DataOutputStream(fos);
            Iterator<NavigationCell> it = cells.iterator();
            
            dos.writeInt(cells.size());
            
            while(it.hasNext())
            {
                NavigationCell nc=it.next();

                int id=cells.indexOf(nc); <-----------------------------------------------------------------------------------------
                dos.write(id);
...
            }
        }
        catch(IOException ex){
           System.out.println("NavMesh '"+fileName+"' could not be saved" );
        }
        finally {
            try {
                if(fos!=null)
                    fos.close();
                if(dos!=null)
                    dos.close();
            } catch (IOException ex) {
                System.out.println("NavMesh '"+fileName+"', file could not be closed" );
            }
        }
        System.out.println("NavMesh saved to '"+fileName+"'");
    }
 
    public static NavigationMesh Load(String fileName)
    {
        FileInputStream is = null;
        DataInputStream dis=null;
        NavigationMesh out= null;
        try {
            is = new FileInputStream(fileName);
            // create new data input stream
            dis = new DataInputStream(is);
         
             int ncells =dis.readInt();
             HashMap<NavigationCell, Integer[]> tempCellsLinks = new HashMap<NavigationCell,Integer[]>();
            
             out= new NavigationMesh();
             for(int i=0;i<ncells;i++)
             {
                 int id=dis.read(); <-----------------------------------------------------------------------------------------
...                 
                 out.AddCell(id,cell);
             }
            
             Iterator<NavigationCell> it = tempCellsLinks.keySet().iterator();
             while(it.hasNext())
             {
                NavigationCell cell = it.next();
                Integer[] links=tempCellsLinks.get(cell);
                cell.setLinks(out.getCell(links[0]),out.getCell(links[1]),out.getCell(links[2]));
             }
        } catch (FileNotFoundException ex) {
            System.out.println("NavMesh '"+fileName+"', file could not be found" );
        } catch (IOException ex) {
            System.out.println("NavMesh '"+fileName+"', something worng happened reading file" );
        } finally {
            try {
            if(is!=null)
               is.close();
            if(dis!=null)
               dis.close();
            } catch (IOException ex) {
                Logger.getLogger(NavigationMesh.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    
        System.out.println("NavMesh file '"+fileName+"' read successfully");
        return out;
    }

private void AddCell(int id,NavigationCell cell) 
    {
        cells.add(/*id,*/cell); 
    }

[rompelstilchen]

well as I said, the list gets its order inverted
so if 1 2 3 4 5 , then 5 4 3 2 1
just as if I was doing list.add(0,data)

[rompelstilchen]

ok I figured out write() saves byte instead of integer, that was the issue
my bad

[JosAH]

It's time to use the poor man's debugger: print out the ids when you save them and print out the ids when you load them again; there must be something fishy going on ...

kind regards,

Jos

[JosAH]

ok I figured out write() saves byte instead of integer, that was the issue
my bad

But you'e using DataOutput/InputStreams; they write and read 4 byte integers ...

kind regards,

Jos

[Norm]

Is that the writeInt() method vs the write() method?

[JosAH]

Is that the writeInt() method vs the write() method?

Grmbl, I missed that one completely; I'm going to drink a Grolsch beer ...

kind regards,

Jos

[Norm]

Have one for me.

[JosAH]

Consider it done.

kind regards,

Jos

[DarrylBurke]

Why did I have to read this when I'm out of beer?

d[ry]b

[JosAH]

Rule #1: never, ever, run out of beer; my liquor store owner is a very nice man: he refills my supply of Grolsch every week; he always puts new a crate in my barn so I never have to be afraid to run out of anything ...

kind regards,

Jos

[rompelstilchen]

try Chimay blue, my favourite, but dont know if its available everywhere :-)