ファイル書き込みの謎

public class Test9 {
    public static void main(String[] args) {
        String inPath = "D:\\in.txt";
        String outPath = "D:\\out.txt";

        BufferedInputStream in = null;
        BufferedOutputStream out = null;
        try {
            in = new BufferedInputStream(new FileInputStream(inPath));
            out = new BufferedOutputStream(new FileOutputStream(outPath));

            byte b[] = new byte[0x10000];
            for(int read = -1; (read = in.read(b, 0, b.length)) != -1;) {
                out.write(b, 0, read);
            }
            out.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                in.close();
                out.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}