按特定条件在列表中查找对象

Question

我有一个清单，必须找到具体的对象。我必须按学生平均价值排序列表，并创建函数来搜索具有第二高价值的学生。如果与其他学生重复，则按函数返回较小的学生。这个任务的另一个要求（要妥善解决）是我不能创建任何对象。下面我留下了我正在使用的类的代码：

import java.time.LocalDate;
import java.util.Comparator;
import java.util.List;

public class Student implements Comparator<Student>{
private String firstName;
private String lastName;
private LocalDate dateOfBirth;
private double averageMark;

public double getAverageMark() {
    return averageMark;
}

   
//function below must find student that I described upper. Currently 
//function is incomplete because I still try to find correct solution 
public static Student findSecondBestStudent(List<Student> students) {


    return students.stream().sorted(Comparator.reverseOrder());
}

@Override
public int compare(Student o1, Student o2) {
    return (int) (o1.getAverageMark() - o2.getAverageMark());
}
}

现在，我尝试通过对stream进行反向排序来解决这个问题，然后移除stream的第一个值，并比较stream的两个下一个对象并返回正确的一个。我可以使用for循环来解决它，但是这个解决方案与任务的条件不匹配（需要创建对象）

Answer 1

实现comparable而不是comparator。

使compareTo函数按所需顺序对学生进行排序（相反）

对流进行排序，跳过1个条目，返回下一个条目。

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

public class Student implements Comparable<Student> {
  private String firstName;
  private String lastName;
  private LocalDate dateOfBirth;
  private double averageMark;
  
  public Student(String firstName, String lastName, LocalDate dateOfBirth, double averageMark) {
    super();
    this.firstName = firstName;
    this.lastName = lastName;
    this.dateOfBirth = dateOfBirth;
    this.averageMark = averageMark;
  }

  public double getAverageMark() {
    return averageMark;
  }

  //function below must find student that I described upper. Currently 
  //function is incomplete because I still try to find correct solution 
  public static Student findSecondBestStudent(List<Student> students) {
    return students.stream().sorted().skip(1).findFirst().orElse(null);
  }

  @Override
  public int compareTo(Student other) {
    if (other == null)
      return 1;
    if (other.averageMark == averageMark) {
      if (other.dateOfBirth == null)
        return -1;
      return other.dateOfBirth.compareTo(dateOfBirth);
    }
    return Double.compare(other.averageMark, averageMark);
  }

  @Override
  public String toString() {
    return "Student [firstName=" + firstName + ", lastName=" + lastName + ", dateOfBirth=" + dateOfBirth
        + ", averageMark=" + averageMark + "]";
  }
  
  public static void main(String[] args) {
    final List<Student> students = new ArrayList<>(6);
    students.add(new Student("Peter", "Tibbitts", LocalDate.of(2001, 4, 6), 5));
    students.add(new Student("Leon", "Gaston", LocalDate.of(1951, 6, 17), 12));
    students.add(new Student("Eric", "Carter", LocalDate.of(1945, 12, 24), 9));
    students.add(new Student("Richard", "Heard", LocalDate.of(1984, 5, 9), 4));
    students.add(new Student("Frankie", "Bonner", LocalDate.of(1970, 4, 19), 10));
    students.add(new Student("Donald", "Pascal", LocalDate.of(2000, 3, 26), 10));
    
    final Student result = Student.findSecondBestStudent(students);
    System.out.println(result);
  }
  
}