无法使用Arrays.sort（）对对象数组进行排序

Question

所以在这个类中我试图创建一个Starship对象数组，然后使用Arrays.sort按长度排序，在前后打印数组。我的Comparable实现似乎是正确的，我提供了compareTo（）方法，但是我收到了以下错误，好像我没有提供正确的实现：

Exception in thread "main" java.lang.ClassCastException: Starship cannot be cast to java.lang.Comparable
at java.util.ComparableTimSort.countRunAndMakeAscending(ComparableTimSort.java:320)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:188)
at java.util.Arrays.sort(Arrays.java:1246)
at Starship.main(Starship.java:44)

我到处都搜索过，但没有发现这个问题。很多，非常感谢任何可以帮助我的代码的人！

import java.util.*;
public class Starship implements Comparable<Starship> {
//fields
private String name;
private String captain;
private int length;
//methods
public Starship (String name, String captain, int length){
    this.name=name;
    this.captain=captain;
    this.length=length;
}
public String getName(){
    return name;
}
public String getCaptain(){
    return captain;
}
public int getLength(){
    return length;
}
public String toString(){
    return "(ship="+name+", captain="+captain+", length="+length+"m)";
}

@Override
public int compareTo (Starship other){
    if (length<other.length) return -1;
    else if(length>other.length) return 1;
    else return 0;
}
//test


public static void main(String[] args){
    Starship[] ships= { 
                       new Starship("Enterprise-D", "Jean-Luc Picard", 643), 
                       new Starship("Serenity", "Malcolm Reynolds", 82),
                       new Starship("Galactica", "William Adama", 1445), 
                       new Starship("Millennium Falcon", "Hans Solo", 35)
                       };
    System.out.println("The ships:");
    for(int i=0; i<4; i++){
        System.out.println(ships[i].toString());
    }

    Arrays.sort(ships);

    System.out.println("After sorting:");
    for(int i=0; i<4; i++){
    System.out.println(ships[i].toString());
    }


}
}