android create folder

mkdir() can only create one level of directories.  

mkdirs(), to create multi-level directories

private final String APP_FOLDER = "/sdcard/DownDemo/"; // sd card application directory
File folder = null;
folder = new File(Environment.getExternalStorageDirectory()+ File.separator + APP_FOLDER );
                if (!folder.exists()) {
                    folder.mkdirs();
                }
private final String APP_FOLDER = "DownDemo"; // sd card application directory
folder = new File(Environment.getExternalStorageDirectory()+ File.separator + APP_FOLDER );
                if (!folder.exists()) {
                    folder.mkdir();
                }