public void copy(View view) {
        File source = new File("storage/emulated/0/test.apk");
        File dest = new File("storage/emulated/0/test_copy.apk");
        try {
            copyFileUsingStream(source, dest);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void copyFileUsingStream(File source, File dest) throws IOException {
        InputStream is = null;
        OutputStream os = null;
        try {
            is = new FileInputStream(source);
            os = new FileOutputStream(dest);
            byte[] buffer = new byte[1024];
            int length;
            while ((length = is.read(buffer)) > 0) {
                os.write(buffer, 0, length);
            }
        } finally {
            is.close();
            os.close();
        }
    }

    public void delete(View view) {
        File dest = new File("storage/emulated/0/test_copy.apk");
        dest.delete();
    }


    public void list(View view) {
        File source = new File("storage/emulated/0/");
        String[] list = source.list();
        for (String s : list) {
            Log.d("ASWIN", "list: "+s);
        }
    }