return a Collection (Set or List)

The scanFile method returns a List. Sometimes, however, I want it to
return a Set. When I change the return type to Collection I get an error:

a00720398/data/BedAndBreakfast.java:33: incompatible types
found : java.util.Collection<a00720398.data.Guest>
required: java.util.List<a00720398.data.Guest>
        guests = console.scanFile(new File("Guests.txt"), new GuestFactory
());
                                 ^
1 error

I've seen Collection used as a parameter in a signature, can it also be
used as a return type? A quick Google seems to show "yes". Is there a
better way of getting the most out of this method?

thufir@arrakis:~/bcit-comp2611-project1$
thufir@arrakis:~/bcit-comp2611-project1$ cat src/a00720398/ui/Console.java
/**
 * Console.java
 */

package a00720398.ui;

import java.util.*;
import java.io.*;
import a00720398.data.*;
import a00720398.interfaces.*;
import a00720398.util.*;

public class Console {

        public Console(){}

        public <T> List<T> scanFile(File file, Factory<T> factory) {
                List<String> lines = new ArrayList<String>();
                List<T> list = new ArrayList<T>();
                try {
                        Scanner scanner = new Scanner(file);
                        while (scanner.hasNextLine()) {
                                String line = scanner.nextLine();
                                        try {
                                                T object = factory.make
(line);
                                                list.add(object);
                                        } catch (DataException e) {
                                                e.printStackTrace();
                                        }
                        }
                } catch (FileNotFoundException e) {
                        e.printStackTrace();
                }
                return list;
        }

        public void output(List<?> objects, File f){
                try {
                        RandomAccessFile file = new RandomAccessFile(f,
"rw");
                        try {
                                file.seek(file.length
()); //go to end of file
                                file.writeUTF(objects.toString()); //
append the collection
                        } catch (IOException e) {
                                e.printStackTrace();
                        }
                } catch (FileNotFoundException e) {
                        e.printStackTrace();
                }
        }

}
thufir@arrakis:~/bcit-comp2611-project1$
thufir@arrakis:~/bcit-comp2611-project1$

thanks,

Thufir