Collections.sort()

import java.util.ArrayList;
import java.util.Collections;
public class Order
{
    private ArrayList<Song> arraylist;

    public Order()
    {
        arraylist = new ArrayList<Song>();
    }
    public void addSong(Song songs)
    {

        arraylist.add(songs);
       
        Collections.sort(arraylist);

    }
    public void printName()
    {      
        for(Song song : arraylist)
        {
            System.out.println(song.getName());
        }
    }
}

Collections.sort(arraylist);那句说找不到符号..是怎么回事?!