Question

我有一个包含主题ArrayList的HashMap。每个学生都有不同的笔记。如何从HashMap打印这些笔记？在我的代码末尾，我有println，如果我想打印某个主题的特定平均值，我该怎么做？

Student student1 = new Apprentice("Jack", "Morgan");
Subject english = new Subject("English", Arrays.asList(2, 3, 2, 2));
Subject japanese = new Subject("japanese", Arrays.asList(2, 2, 2, 4));

HashMap<Student, List<Subject>> studentGrade = new HashMap<>();
studentGrade.put(student1, Arrays.asList(english, japanese));

for (Map.Entry<Apprentice, List<Subject> > entry : apprenticeGrades.entrySet()) {
    System.out.println("Student " + entry.getKey());

    for (Subject subject : entry.getValue()) {
        System.out.println("Average from subject:" + subject.getAvg());
    }

Answer 1

 final List<Subject> subjectList = studentGrade
                // get a Collection<List<Subject>>
                .values()
                // make a stream from the collection
                .stream()
                // turn each List<Subject> into a Stream<Subject> and merge these streams
                .flatMap(List::stream)
                // accumulate the result into a List
                .collect(Collectors.toList());

        for(Subject subject : subjectList){
            System.out.println("Average from subject:" + subject.getAvg());
        }

首先将所有主题（值）放入列表中并迭代它以计算并打印平均值。

打印作为HashMap值的ArrayLists

1 个答案: