code: public int getFontNumber(RtfFont font) {
          if(font instanceof RtfParagraphStyle) {
              font = new RtfFont(this.document, font);
          }
          int fontIndex = -1;
          for(int i = 0; i < fontList.size(); i++) {
              if(fontList.get(i).equals(font)) {
                  fontIndex = i;
              }
          }
          if(fontIndex == -1) {
              fontIndex = fontList.size();
              fontList.add(font);
          }
          return fontIndex;
      }
docs: Gets the index of the font in the list of fonts. If the font does not
  exist in the list, it is added.
  
  @param font The font to get the id for
  @return The index of the font