public class Begin {
    public static void main(String[] args) {
        Image image = new Image();
        List<String> list = new ArrayList<String>();
        list.add("1.jpg");
        list.add("5.jpg");
        list.add("2.jpg");
        list.add("7.jpg");
        list.add("6.jpg");
        list.add("9.jpg");
        image.setUrls(list);
        for (int i = 0; i < 3; i++) {
            ImageDFile imageDFile = new ImageDFile(image);
            imageDFile.start();
        }
    }
}

public class ImageDFile extends Thread {
    public Image image;
    public ImageDFile(Image image) {
        this.image = image;
    }

    @Override
    public void run() {
        List<String> list = image.getUrls();
        for (int i = 0; i < list.size(); i++) {
            if (list.size() > 0) {
                System.out.println(list.get(i) + "---" + Thread.currentThread().getName());
                list.remove(i);
            }
        }
    }
}