在Java中使用比较器比较对象属性
我正在做DS/A作业,我一辈子都不知道如何使用Comparable/Comparator接口将对象的特定属性标记为比较和排序的键。我们正在使用一个提供给我们的Mergesort函数,我相信除了我收到的这个错误之外,我已经在程序中完成了大部分其他工作:在Java中使用比较器比较对象属性,java,comparable,Java,Comparable,我正在做DS/A作业,我一辈子都不知道如何使用Comparable/Comparator接口将对象的特定属性标记为比较和排序的键。我们正在使用一个提供给我们的Mergesort函数,我相信除了我收到的这个错误之外,我已经在程序中完成了大部分其他工作: incompatible types: Student[] cannot be converted to Comparable[] 我非常希望能够深入了解这个问题,因为我对Java和OOP还是相当陌生的。以下是我得到的: Test
incompatible types: Student[] cannot be converted to Comparable[]
我非常希望能够深入了解这个问题,因为我对Java和OOP还是相当陌生的。以下是我得到的:
TestMergeSort.java:
public class TestMergeSort {
public static void main(String[] args) {
Student[] students = initializeStudentsArray();
System.out.println("Displaying students array before sorting...");
display(students);
System.out.println("Being sorting...");
/*
* The Student array will be sorted by studentId
* which is declared as a String
*/
Merge.sort(students); // TODO: Fix the Student class to eliminate this error
System.out.println("End sorting...");
System.out.println("Displaying students array after sorting...");
display(students);
}
private static Student[] initializeStudentsArray() {
Student[] students = new Student[5];
students[0] = new Student("Joe", "Jones", "1001");
students[1] = new Student("Adam", "Ant", "950");
students[2] = new Student("Bill", "Barnes", "735");
students[3] = new Student("Mark", "Roth", "1102");
students[4] = new Student("Jerome", "Howard", "1150");
return students;
}
private static void display(Student[] students) {
for (Student std : students) {
System.out.println("Students [firstName=" + std.firstName + ", lastName=" + std.lastName + ", studentId=" + std.studentId + "]");
}
}
}
和Student.java:
public class Student implements Comparator<Student> {
public String firstName;
public String lastName;
public String studentId;
public Student(String first, String last, String Id) {
this.firstName = first;
this.lastName = last;
this.studentId = Id;
}
@Override
public int compare(Student stud1, Student stud2) {
String student1 = stud1.studentId;
String student2 = stud2.studentId;
return student1.compareTo(student2);
}
}
公共类学生实现比较器{
公共字符串名;
公共字符串lastName;
公共字符串学生ID;
公立学生(字符串第一,字符串最后,字符串Id){
this.firstName=first;
this.lastName=last;
this.studentId=Id;
}
@凌驾
公共整数比较(学生学习1、学生学习2){
字符串student1=stud1.studentId;
字符串student2=stud2.studentId;
返回学生1.与(学生2)进行比较;
}
}
我可能做错了什么,所以请给我一点提示。非常感谢您抽出时间
Merge.sort(students);
我不知道合并类是什么。我只使用默认的Collections.sort(…)
我不知道合并类是什么。我只使用默认的Collections.sort(…)
您的学生班级应实施可比较和非比较。您的学生班级应实施可比较和非比较。
public class Student implements Comparator<Student> {
/*
** Use the Collections API to sort a List for you.
**
** When your class has a "natural" sort order you can implement
** the Comparable interface.
**
** You can use an alternate sort order when you implement
** a Comparator for your class.
*/
import java.util.*;
public class Person implements Comparable<Person>
{
String name;
int age;
public Person(String name, int age)
{
this.name = name;
this.age = age;
}
public String getName()
{
return name;
}
public int getAge()
{
return age;
}
public String toString()
{
return name + " : " + age;
}
/*
** Implement the natural order for this class
*/
public int compareTo(Person p)
{
return getName().compareTo(p.getName());
}
static class AgeComparator implements Comparator<Person>
{
public int compare(Person p1, Person p2)
{
return p1.getAge() - p2.getAge();
}
}
public static void main(String[] args)
{
List<Person> people = new ArrayList<Person>();
people.add( new Person("Homer", 38) );
people.add( new Person("Marge", 35) );
people.add( new Person("Bart", 15) );
people.add( new Person("Lisa", 13) );
// Sort by natural order
Collections.sort(people);
System.out.println("Sort by Natural order");
System.out.println("\t" + people);
// Sort by reverse natural order
Collections.sort(people, Collections.reverseOrder());
System.out.println("Sort by reverse natural order");
System.out.println("\t" + people);
// Use a Comparator to sort by age
Collections.sort(people, new Person.AgeComparator());
System.out.println("Sort using Age Comparator");
System.out.println("\t" + people);
// Use a Comparator to sort by descending age
Collections.sort(people, Collections.reverseOrder(new Person.AgeComparator()));
System.out.println("Sort using Reverse Age Comparator");
System.out.println("\t" + people);
// Use a Comparator with lambda expression to sort by age
// Collections.sort(people, (o1, o2) -> o1.getAge() - o2.getAge());
// Collections.sort(people, Comparator.comparingInt(p -> p.getAge()));
Collections.sort(people, Comparator.comparingInt(Person::getAge));
System.out.println("Sort using Lambda Age Comparator");
System.out.println("\t" + people);
}
}