code: public String readLine() throws IOException {
          StringBuffer buf = new StringBuffer(80);
          int line = mLineNumber;
          int c;
          while (line == mLineNumber && (c = read()) >= 0) {
              buf.append((char)c);
          }
          return buf.toString();
      }
docs: After calling readLine, calling getLineNumber returns the next line
  number.