java Lambda表达式如何按条件动态传入方法引用？

  • Z时代
  • 2024-03-11
  • 分类：IT

java中如何按条件传入分组
例如有个学生类集合，如何动态传入一个方法引用来分组？

list.stream().collect(Collectors.groupingBy(Student::getSex));
list.stream().collect(Collectors.groupingBy(Student::getAge));
public List<Student> test(动态传入){
// ...list
list.stream().collect(Collectors.groupingBy(动态传入));
return list
}

回答：

public static List<Student> groupBy(List<Student> list, Function<Student, ?> dynamicReference) {
    Map<?, List<Student>> groupedStudents = list.stream()
        .collect(Collectors.groupingBy(dynamicReference));
    return groupedStudents.values().stream()
            .flatMap(Collection::stream)
            .collect(Collectors.toList());
}
public static void main(String[] args) {
    List<Student> students = Arrays.asList(
            new Student("Alice", "female", 20),
            new Student("Bob", "male", 22),
            new Student("Charlie", "male", 23),
            new Student("Alice", "female", 21),
            new Student("Bob", "male", 22)
    );
    List<Student> groupedBySex = groupBy(students, Student::getSex);
    List<Student> groupedByAge = groupBy(students, Student::getAge);
    System.out.println(Arrays.toString(groupedBySex.toArray()));
    System.out.println(Arrays.toString(groupedByAge.toArray()));
}

回答：

参数传一个Function,代码如下

public static Map<String, List<Student>> process(Function<Student, String> function) {
    List<Student> studentList = new ArrayList<>();
    Map<String, List<Student>> map = studentList.stream().collect(Collectors.groupingBy(function));
    return map;
}
public static void main(String[] args) {
    Map<String, List<Student>> map=process(Student::getName);
}

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