code: @Override
      protected final char nextGoodChar() {
          char c = nextChar();
          if (c > ' ' || c == 0) return c; // 0 表示buffer结尾了
          for (;;) {
              c = nextChar();
              if (c > ' ' || c == 0) return c;
          }
      }
docs: 读取下一个有效字符
  
  @return 有效字符