code: public void setButtonSize(int size) {
          if (size != SIZE_NORMAL && size != SIZE_MINI) {
              throw new IllegalArgumentException("Use @FabSize constants only!");
          }
  
          if (mFabSize != size) {
              mFabSize = size;
              updateBackground();
          }
      }
docs: Sets the size of the <b>FloatingActionButton</b> and invalidates its layout.
  
  @param size size of the <b>FloatingActionButton</b>. Accepted values: SIZE_NORMAL, SIZE_MINI.