Java Array Index Out Of Bounds Exception: -1

Alright , I have a problem which I can't figure out whats wrong. So I have jList and List . I need a function that when I click on item (in jList any item ) and it would change in my label icon , (I'm dealing with images). It works somehow, it changes my label icon to the image I pick from jList, but it throws me Exception and the program crashes , usually first 2 items cause no errors , third and further items cause it. After it crashes and throws me bunch of red text , I can still change my icon.

This is the function where I get the images and add them to List (adding path to them)

private static void getImages(String src) throws IOException {
    //Exctract the name of the image from the src attribute
    int indexname = src.lastIndexOf("/");

    if (indexname == src.length()) {
        src = src.substring(1, indexname);
    }

    indexname = src.lastIndexOf("/");
    String name = src.substring(indexname, src.length());

    //Open a URL Stream
    URL url = new URL(src);
    InputStream in = url.openStream();

    GPath=fPath+name;
    OutputStream out = new BufferedOutputStream(new FileOutputStream( GPath));
    //Im adding to the list string (link to image) here
    imagesListN.add(GPath);

    System.out.println("list size: "+imagesListN.size());


    for (int b; (b = in.read()) != -1;) {

        out.write(b);
    }

    out.close();
    in.close();

}

It adds them normally . Yes I'm downloading them , that's why I want to see them once they are downloaded.

This is where I click on jList function.

     list.addListSelectionListener(new ListSelectionListener() {

        private int a;

        @Override
        public void valueChanged(ListSelectionEvent arg0) {
            if (!arg0.getValueIsAdjusting()) {
                String h;
                int k;
                k = list.getSelectedIndex();
                System.out.println("List id: "+k);
                a = Main.imagesListN.indexOf(k);
                System.out.println("imagesListN id: "+a);

                h = Main.imagesListN.get(k);
                System.out.println("h : "+h);
                ImageIcon img = new ImageIcon(h);

                imageReview.setIcon(img);
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    });

Here is the jList (name list) . Exception is at

a = Main.imagesListN.indexOf(k);

it gives me -1 , but the h = Main.imagesListN.get(k); gives me the link I need and gives it to ImageIcon img = new ImageIcon(h); and then imageReview.setIcon(img); . Label icon changes everytime when I click on item I need. Maybe it's not a = Main.imagesListN.indexOf(k); that I'm looking at , but something gives me -1. Btw I'm excecuting everything in Thread.

`public class Crawler extends Thread {

Main main = new Main();

public void run(){
        try {
                main.download();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

}`

nothing fancy here. Each functions are in there own class , getImages() is in main , listListener is in class Langas (Class where are all buttons,labels , etc. are created nothing else) and Thread well , Thread. Also it works fine after everything is downloaded , no exceptions . Error appears durring downloading proccess