我有这个比较器，比较每个标记的标记，并从最高到最低排序。唯一的问题是主题列表绑定在学生对象中。所以每个学生都有很多科目。总标记为double型。比较器不能正常工作。
public class RankComparator implements Comparator<Subject> {
@Override
public int compare(Subject s1, Subject s2) {
if (s1.getoveralMark() < s2.getoveralMark())
return -1;
if (s1.getoveralMark() > s2.getoveralMark())
return 1;
return 0;
}
}
更新：我添加了以下代码，但仍然没有按最高的overalMark排序主题。
for (Student student : studentList) {
// if (subj.subjectName.contains("English")) {
for (Subject subj : student.subject) {
Collections.sort(student.subject, new RankComparator());
System.out.println(subj.overalMark);
}
Collections.sort(studentList, compareByAllSubjects());
for (Student student : studentList) {
System.out.println(student.firstName);
for (Subject subk : student.subject) {
System.out.println(subk.subjectName);
System.out.println(subk.overalMark);
}
}
// }
}
private static Comparator<Student> compareBySubject(final int index) {
return new Comparator<Student>() {
@Override
public int compare(Student student0, Student student1) {
Subject subject0 = student0.subject.get(index);
Subject subject1 = student1.subject.get(index);
if (subject0.getSubjectName() == subject1.getSubjectName()) {
double mark0 = subject0.getoveralMark();
double mark1 = subject1.getoveralMark();
return Double.compare(mark0, mark1);
}
return 0;
}
};
}
private static double computeMaxMark(List<Subject> subjects) {
double max = -Double.MAX_VALUE;
for (Subject subject : subjects) {
max = Math.max(max, subject.getoveralMark());
}
return max;
}
private static Comparator<Student> compareByAllSubjects() {
return new Comparator<Student>() {
@Override
public int compare(Student student0, Student student1) {
double mark0 = computeMaxMark(student0.getSubject());
double mark1 = computeMaxMark(student1.getSubject());
return Double.compare(mark0, mark1);
}
};
}
答案 0 :(得分：0)
因此，根据评论，您希望根据学生在一个科目中取得的成绩对学生进行排序。在这种情况下，您不需要Comparator<Subject>而是Comparator<Student> - 即比较学生的比较器。
然而，这个比较器必须知道＆＃34;根据哪个学科应该比较学生。在这种情况下，可能有必要知道所有学生是否具有相同的科目，或者每个学生的科目组是否可能不同。如果它们可能不同，则必须考虑排序应如何处理不具有学生应根据其分类的学生。
但是，在此示例中显示了创建比较器的一般方法，该比较器基于他们在特定主题中实现的标记对学生进行排序：
（编辑：添加了另一个排序标准，这似乎是一个猜谜游戏....）
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Random;
public class StudentSorting
{
public static void main(String[] args)
{
Random random = new Random(0);
List<Student> students = new ArrayList<Student>();
for (int i=0; i<3; i++)
{
Student student = new Student("Student"+i);
student.addSubject(new Subject("A", random.nextInt(6)));
student.addSubject(new Subject("B", random.nextInt(6)));
student.addSubject(new Subject("C", random.nextInt(6)));
students.add(student);
}
for (int s=0; s<3; s++)
{
System.out.println("Students compared by subject "+s);
Collections.sort(students, compareBySubject(s));
for (Student student : students)
{
System.out.println(" "+student);
}
}
System.out.println("Students compared all subjects");
Collections.sort(students, compareByAllSubjects());
for (Student student : students)
{
System.out.println(" "+student);
}
}
/**
* Creates a comparator that compares students by the overall mark
* that they achieved in the subject with the given index
*
* @param index The index of the subject
* @return The comparator
*/
private static Comparator<Student> compareBySubject(final int index)
{
return new Comparator<Student>()
{
@Override
public int compare(Student student0, Student student1)
{
Subject subject0 = student0.getSubject(index);
Subject subject1 = student1.getSubject(index);
double mark0 = subject0.getOverallMark();
double mark1 = subject1.getOverallMark();
return Double.compare(mark0, mark1);
}
};
}
/**
* Creates a comparator that compares students by the overall mark
* that they achieved in any subject
*
* @return The comparator
*/
private static Comparator<Student> compareByAllSubjects()
{
return new Comparator<Student>()
{
@Override
public int compare(Student student0, Student student1)
{
double mark0 = computeMaxMark(student0.getSubjects());
double mark1 = computeMaxMark(student1.getSubjects());
return Double.compare(mark0, mark1);
}
};
}
/**
* Computes the maximum overall mark of the given subjects
*
* @param subjects The subjects
* @return THe maximum mark
*/
private static double computeMaxMark(List<Subject> subjects)
{
double max = -Double.MAX_VALUE;
for (Subject subject : subjects)
{
max = Math.max(max, subject.getOverallMark());
}
return max;
}
}
class Subject
{
private final String name;
private final double mark;
Subject(String name, double mark)
{
this.name = name;
this.mark = mark;
}
double getOverallMark()
{
return mark;
}
@Override
public String toString()
{
return name+"("+mark+")";
}
}
class Student
{
private final String name;
private final List<Subject> subjects;
Student(String name)
{
this.name = name;
this.subjects = new ArrayList<Subject>();
}
void addSubject(Subject subject)
{
subjects.add(subject);
}
Subject getSubject(int index)
{
return subjects.get(index);
}
List<Subject> getSubjects()
{
return subjects;
}
@Override
public String toString()
{
return name+" with "+subjects;
}
}