code: private void fetchSystemStyle() throws IOException {
          String url = "https://android.googlesource.com/platform/frameworks/base/+/master/api/current.txt";
          String html = getUrl(url);
          String code = retrieveCode(html);
          if (code == null) {
              System.err.println("code area not found");
              return;
          }
          int begin = code.indexOf("R.style");
          int end = code.indexOf("}", begin);
          String styleCode = code.substring(begin, end);
          String[] lines = styleCode.split("\n");
          for (String line : lines) {
              line = line.trim();
              if (line.startsWith("field public static final")) {
                  line = Strings.substringBefore(line, ";").replace("deprecated ", "")
                          .substring("field public static final int ".length()).replace("_", ".");
                  System.out.println(line);
              }
          }
      }
docs: from https://android.googlesource.com/platform/frameworks/base/+/master/api/current.txt r.style section