早上看了这样的一坨代码（一些业务信息我抹去了，不用太在意具体上面这些filter的具体行为，firstname和lastname也是替代了原始的字段）

可以作为一个很好的重构实例。我其实并不知道这段代码要干什么，但是即便如此，我们也可以重构代码

第一眼完全看不懂在写什么

   private static final String FILTER_OR = "firstName='%s' or lastName='%s'";

  private static final String FILTER_AND = "firstName='%s' and lastName='%s'";

  private static final String FILTER_OR_CON = "firstName='%s' or lastName='%s' con";

  private static final String FILTER_AND_CON = "firstName='%s' and lastName='%s' con";

  private static final String FILTER_USER_ID_NAME = "firstName='%s' and lastName='%s' and userId";

 private String filterBuilder_original(List<List<String>> searchcriterias) {
    StringBuilder filters = new StringBuilder();

    for (int i = 0; i < searchcriterias.size(); i++) {

       // 第一行如果要特殊处理，那就单独拿出来
       // 双层if的逻辑是肯定可以改写的
      if (i == 0) {
      //searchcriterias.get(i)代码是重复代码，而且get出来是什么东西，不知道
      // searchcriterias.get(i).get(0)这个不知道是什么的东西get出来的这个东西是什么东西？也不知道
      // 至于0和1完全就是一个魔法值，不知道具体的含义，第一个index是什么，第二个是什么？是只有这两个index吗？
        if (searchcriterias.get(i).get(0).equals(searchcriterias.get(i).get(1))) {
          filters.append(
              String.format(
                  FILTER_OR, searchcriterias.get(i).get(0), searchcriterias.get(i).get(1)));
        } else {
        // String命名为a。。。
          String a =
              String.format(
                  FILTER_AND, searchcriterias.get(i).get(0), searchcriterias.get(i).get(1));
          filters.append(a);
        }
      } else {
        if (searchcriterias.get(i).get(0).equals(searchcriterias.get(i).get(1))) {
          filters.append(
              String.format(
                  FILTER_OR_CON, searchcriterias.get(i).get(0), searchcriterias.get(i).get(1)));
        } else {
          filters.append(
              String.format(
                  FILTER_AND_CON, searchcriterias.get(i).get(0), searchcriterias.get(i).get(1)));
        }
      }
    }

    // 这行用的信息和第一行一样
    // 需要指出的是这段代码没有考虑到链表为空的情况，是否在上层有判断，我无法得知，但就这段代码而言，如果list为null会空指针错误
    filters.append(
        String.format(
            FILTER_USER_ID_NAME, searchcriterias.get(0).get(0), searchcriterias.get(0).get(1)));

    return filters.toString();
  }

改完的版本

  private static final String FILTER_OR = "firstName='%s' or lastName='%s'";

  private static final String FILTER_AND = "firstName='%s' and lastName='%s'";

  private static final String FILTER_OR_CON = "firstName='%s' or lastName='%s' con";

  private static final String FILTER_AND_CON = "firstName='%s' and lastName='%s' con";

  private static final String FILTER_USER_ID_NAME = "firstName='%s' and lastName='%s' and userId";

  private static final int FIRST_NAME_INDEX = 0;
  private static final int LAST_NAME_INDEX = 1;

  private String filterBuilder(List<List<String>> searchLists) {
    int size = searchLists.size();
    if (size == 0) {
      return "";
    }

    StringBuilder filters = new StringBuilder();

    List<String> firstRow = searchLists.get(0);
    String firstName = firstRow.get(FIRST_NAME_INDEX);
    String lastName = firstRow.get(LAST_NAME_INDEX);

    String lastRow = String.format(FILTER_USER_ID_NAME, firstName, lastName);

    if (firstName.equals(lastName)) {
      filters.append(String.format(FILTER_OR, firstName, lastName));
    } else {
      filters.append(String.format(FILTER_AND, firstName, lastName));
    }

    for (int i = 1; i < size; i++) {
      List<String> crrRow = searchLists.get(i);
      firstName = crrRow.get(FIRST_NAME_INDEX);
      lastName = crrRow.get(LAST_NAME_INDEX);

      if (firstName.equals(lastName)) {
        filters.append(String.format(FILTER_OR_CON, firstName, lastName));
      } else {
        filters.append(String.format(FILTER_AND_CON, firstName, lastName));
      }
    }

    filters.append(lastRow);

    return filters.toString();
  }