Java流中的三元操作员

Question

我具有以下功能，该功能利用流和收集器来创建映射和基于布尔的执行中的不同之

private Map<Integer, Long> getCountPerAnswerChoice(boolean isMultiSelectableQuiz, int questionId, List<QuizResponse> quizResponses) {
     return isMultiSelectableQuiz
        ? quizResponses.stream()
            .flatMap(response -> response.getAnswersByQuestions().stream())
            .filter(answerByQuestion -> answerByQuestion.getQuestionId() == questionId)
            .collect(
                Collectors.flatMapping(
                    (QuizQuestionAnswer answerByQuestion) -> answerByQuestion.getAnswerSelectionsList().stream(),
                    Collectors.groupingBy(selection -> selection, Collectors.counting())))
        : quizResponses.stream()
            .flatMap(response -> response.getAnswersByQuestions().stream())
            .filter(answerByQuestion -> answerByQuestion.getQuestionId() == questionId)
            .collect(
                Collectors.groupingBy(QuizQuestionAnswer::getAnswerSelection, Collectors.counting()));
    }

处如果/其他分支，

quizResponses.stream()
            .flatMap(response -> response.getAnswersByQuestions().stream())
            .filter(answerByQuestion -> answerByQuestion.getQuestionId() == questionId)

我是否尝试过移动iSmultSelection？ ：在collect（）中选中

private Map<Integer, Long> getCountPerAnswerChoice(boolean isMultiSelectableQuiz, int questionId, List<QuizResponse> quizResponses) {
     return quizResponses.stream()
        .flatMap(response -> response.getAnswersByQuestions().stream())
        .filter(answerByQuestion -> answerByQuestion.getQuestionId() == questionId)
        .collect(
            isMultiSelectableQuiz
                ? Collectors.groupingBy(
                    QuizQuestionAnswer::getAnswerSelection, Collectors.counting())
                : Collectors.flatMapping(
                    (QuizQuestionAnswer answerByQuestion) -> answerByQuestion.getAnswerSelectionsList().stream(),
                    Collectors.groupingBy(selection -> selection, Collectors.counting())));
    }

Answer 1

我发现Java编译器很难推断出从流到收集器流动的类型参数。您的两个用例之间的唯一区别是使用的收集器。我会将收集器拉到单独的方法中，以返回每种情况的适当收集器。这不仅有助于清理代码，而且提供收集器的方法的返回类型阐明了类型，避免了错误。

private Map<Integer, Long> getCountPerAnswerChoice(boolean isMultiSelectableQuiz,
        int questionId, List<QuizResponse> quizResponses) {
    return quizResponses.stream()
        .flatMap(response -> response.getAnswersByQuestions().stream())
        .filter(answerByQuestion -> answerByQuestion.getQuestionId() == questionId)
        .collect(getCollectorForQuizType(isMultiSelectableQuiz));
}

private Collector<? super QuizQuestionAnswer, ?, Map<Integer, Long>> getCollectorForQuizType(
        boolean isMultiSelectableQuiz) {
    return isMultiSelectableQuiz
        ? Collectors.groupingBy(QuizQuestionAnswer::getAnswerSelection, Collectors.counting())
        : Collectors.flatMapping(
            answerByQuestion -> answerByQuestion.getAnswerSelectionsList().stream(),
            Collectors.groupingBy(selection -> selection, Collectors.counting()));
}

我什至会考虑将其进一步分解，也许将收藏家存储在田野中，而只是用名字返回。里面的三元人看起来仍然太忙了。或将一个返回一个if块，如果它掉落了，请返回另一个。