can not resolve constructor 'Date()'

   public void onClick(DialogInterface dialog, int which) {
        switch (which){
            case 0:
                Intent takePhotoIntent=new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                mMediaUri=getOutputMediaFileUri(MEDIA_TYPE_IMAGE);
                if(mMediaUri==null){
                    Toast.makeText(MainActivity.this,R.string.error_external_storage,Toast.LENGTH_LONG).show();
                }
                else {
                    takePhotoIntent.putExtra(MediaStore.EXTRA_OUTPUT, mMediaUri);
                    startActivityForResult(takePhotoIntent, TAKE_PHOTO_REQUEST);
                }
                break;
            case 1:
                break;
            case 2:
                break;
            case 3:
                break;
        }
   }
   private Uri getOutputMediaFileUri(int mediaTypeImage) {

       if(isExternalStorageAvailable()){


           String appName=MainActivity.this.getString(R.string.app_name);
           File mediaStorageDir =new File(
                   Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),appName);

            if(! mediaStorageDir.exists()){
                if(! mediaStorageDir.mkdirs()){
                    Log.e(TAG,"Failed to create directory");
                    return null;
                }
            }

           File mediaFile;
           Date now=new Date();
           String timestamp=new SimpleDateFormat("yyyyMMdd_HHmmss",Locale.TAIWAN).format(now);