java - 类不是抽象的，不重写抽象方法问题

Question

我很努力地做到了。但我收到一条错误消息“Student 不是抽象的，也不会重写 Comparable 中的抽象方法compareTo(Object)类 Student 扩展 Person {"

abstract class Person implements Comparable {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class Student extends Person {
    private int id;

    public Student(String name, int id) {
        super(name);

        this.id = id;
    }

    public String toString() {
        return Integer.toString(id);
    }

    public int getId() {
        return this.id;
    }

    @Override
    public int compareTo(Student s) {
        if (this.id < s.getId()) {
            return -1;
        }else if (this.id > s.getId()) {
            return 1;
        }
        return 0;
    }
} 

@Override
    public int compareTo(Student s) {
        if (this.id < s.getId()) {
            return -1;
        }else if (this.id > s.getId()) {
            return 1;
        }
        return 0;
    }

这是我认为有问题的地方......

Answer 1

正如 @Andreas 已经解释的那样，让 Student 实现 Comparable，而不是 Person。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

abstract class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class Student extends Person implements Comparable<Student> {
    private int id;

    public Student(String name, int id) {
        super(name);

        this.id = id;
    }

    public String toString() {
        return Integer.toString(id);
    }

    public int getId() {
        return this.id;
    }

    @Override
    public int compareTo(Student o) {
        return Integer.compare(this.id, o.id);
    }
}

演示

public class Main {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<Student>();
        list.add(new Student("Abc", 321));
        list.add(new Student("Xyz", 12));
        list.add(new Student("Mnp", 123));
        Collections.sort(list);
        System.out.println(list);
    }
}

输出:

[12, 123, 321]