code: public static Builder newBuilder(Context context, int themeResId) {
          if (Build.VERSION.SDK_INT >= 21) {
              return new APi21Builder(context, themeResId);
          }
          return new Api20Builder(context, themeResId);
      }
docs: Create new Builder.
  
  @param context    context.
  @param themeResId theme res id.
  @return {@link Builder}.