Question

我遇到了重复代码的问题，不知道应该如何解决。我有2种几乎相似的方法，以后我知道还会有更多方法。

 public static List<ExamResult> numberOfMarks(List<ExamResult> allMarks, int offset, int records) throws DaoException {
    List<ExamResult> result = new ArrayList<>();
    for (int i = 0; i < allMarks.size(); i++) {
        if (offset == 0) {
            if (i < records) {
                result.add(allMarks.get(i));

            }
        } else if (offset > 0) {
            if (i > offset * records && i < (offset * records + records + 1)) {
                result.add(allMarks.get(i));
            }

        }
    }
    return result;

}

public static List<Question> numberOfQuestions(List<Question> allQuestion, int offset, int records) throws DaoException {
    List<Question> result = new ArrayList<>();
    for (int i = 0; i < allQuestion.size(); i++) {
        if (offset == 0) {
            if (i < records) {
                result.add(allQuestion.get(i));

            }
        } else if (offset > 0) {
            if (i > offset * records && i < (offset * records + records + 1)) {
                result.add(allQuestion.get(i));
            }

        }
    }
    return result;
}

Answer 1

您可以使用“ generic methods”。该方法将是：

public static <T> List<T> extract(List<T> input, int offset, int record) {
    ... //the same code with T instead of Question or Answer
}

Answer 2

“泛型”就是答案。以下是一种可行的方法。

public <T> List<T> numberOfQuestions(List<T> allItems, int offset, int records) {
    List<T> result = new ArrayList<>();
    for (int i = 0; i < allItems.size(); i++) {
        if (offset == 0) {
            if (i < records) {
                result.add(allItems.get(i));

            }
        } else if (offset > 0) {
            if (i > offset * records && i < (offset * records + records + 1)) {
                result.add(allItems.get(i));
            }

        }
    }
    return result;
}

Answer 3

我们可以使用方法List#subList(int fromIndex, int toIndex)来实现您想要的：

public static <T> List<T> getEntries(
    List<T> list,
    final int offset, 
    final int records) {
  final int listSize = list.size();

  final int fromIndex;
  if (offset == 0) {
    fromIndex = 0;
  } else if (offset * records + 1  < listSize) {
    fromIndex = offset * records + 1;
  } else {
    fromIndex = -1;
  }     

  final int toIndex;
  if (offset + records <= listSize) {
    toIndex = offset + records;
  } else {
    toIndex = listSize;
  }

  final List<T> result;
  if (fromIndex >= 0) {
    result = list.subList(fromIndex, toIndex);
  } else {
    result = Collections.emptyList(); // or new ArrayList<T>() if you want to modify the list
  }

  return result;
}

public static List<ExamResult> numberOfMarks(
    List<ExamResult> allMarks,
    final int offset,
    final int records) throws DaoException {
  return getEntries(allMarks, offset, records);
}

public static List<Question> numberOfQuestions(
    List<Question> allQuestions, 
    final int offset,
    final int records) throws DaoException {
  return getEntries(allQuestions, offset, records);
}

如何重构具有不同List <objects>的方法

3 个答案: