Другой вариант, который был упомянут ранее, но не показан в качестве примера, - это реализация специального Comparator для сравнения по классам.
Этот пример состоит из класса Student, реализующего интерфейс IStudent, StudentGradeComparator и небольшого класса Main, который использует образцы данных.
Дополнительные пояснения даются в виде комментариев к коду, пожалуйста, прочитайте их
/**
* A class that compares students by their grades.
*/
public class StudentGradeComparator implements Comparator<IStudent> {
@Override
public int compare(IStudent studentOne, IStudent studentTwo) {
int result;
int studentOneGrade = studentOne.getGrade();
int studentTwoGrade = studentTwo.getGrade();
/* The comparison just decides if studentOne will be placed
* in front of studentTwo in the sorted order or behind
* or if they have the same comparison value and are considered equal
*/
if (studentOneGrade > studentTwoGrade) {
/* larger grade is considered "worse",
* thus, the comparison puts studentOne behind studentTwo
*/
result = 1;
} else if (studentOneGrade < studentTwoGrade) {
/* smaller grade is considered "better"
* thus, the comparison puts studentOne in front of studentTwo
*/
result = -1;
} else {
/* the students have equal grades,
* thus, there will be no swap
*/
result = 0;
}
return result;
}
}
Вы можете применить этот класс в sort(Comparator<? super IStudent> comparator) методе List:
/**
* The main class for trying out the sorting by Comparator
*/
public class Main {
public static void main(String[] args) {
// a test list for students
List<IStudent> students = new ArrayList<IStudent>();
// create some example students
IStudent beverly = new Student("Beverly", 3);
IStudent miles = new Student("Miles", 2);
IStudent william = new Student("William", 4);
IStudent deanna = new Student("Deanna", 1);
IStudent jeanLuc = new Student("Jean-Luc", 1);
IStudent geordi = new Student("Geordi", 5);
// add the example students to the list
students.add(beverly);
students.add(miles);
students.add(william);
students.add(deanna);
students.add(jeanLuc);
students.add(geordi);
// print the list in an unordered state first
System.out.println("———— BEFORE SORTING ————");
students.forEach((IStudent student) -> {
System.out.println(student.getName() + ": " + student.getGrade());
});
/*---------------------------------------*
* THIS IS HOW YOU APPLY THE COMPARATOR *
*---------------------------------------*/
students.sort(new StudentGradeComparator());
// print the list ordered by grade
System.out.println("———— AFTER SORTING ————");
students.forEach((IStudent student) -> {
System.out.println(student.getName() + ": " + student.getGrade());
});
}
}
Просто для полноты, вот интерфейс IStudent и класс его реализации Student:
public interface IStudent {
String getName();
int getGrade();
}
/**
* A class representing a student
*/
public class Student implements IStudent {
private String name;
private int grade;
public Student(String name, int grade) {
this.name = name;
this.grade = grade;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
}