ArrayList.addAll syntax

I have a serializable class that is working just fine, until I try to
read in the only serialized object (an array list) and copy it to the
original arraylist.

The class needs to be able to be used without reading in a serialized
copy, but needs the flexibility of reading one in as well.

The class is called Options and holds key/value pairs in the array
list. The following methods are available:

Options.set(String key, String value), Options.get(String key),
Options.open(String fileName), Options.save(), Options.save(String
fileName), Options.remove(String key)

Everything works fine, but when I try to call the object's .get method
after calling .open() I am thrown a NoSuchFieldException. I am certain
that there is something screwed up with the copying of the serialized
ArrayList to the existing one. I have tried looping through, copying,
..copyAll... None seem to work.

Thanks for any ideas!

Here's the code:
--------------------------------------------------------------------------
package options;

import java.io.*;
import java.util.ArrayList;

public class Options implements Serializable {

    private ArrayList<String[]> preferences;
    private String fileName = null;

    public Options() {
        preferences = new ArrayList<String[]>(10);
    }

    public Options(int defaultSize) {
        preferences = new ArrayList(defaultSize);
    }

    public void open(String fileName) throws FileNotFoundException,
IOException {
        FileInputStream in = new FileInputStream(fileName);
        ObjectInputStream objIn = new ObjectInputStream(in);
        try {
            ArrayList<String[]> tempList =
(ArrayList<String[]>)objIn.readObject();
            preferences.clear();
            preferences.addAll(tempList);

        } catch (ClassNotFoundException ex) {
            throw new FileNotFoundException();
        }
    }

    public void save(String fileName) throws IOException {
        writeFile(fileName);
    }

    public void save() throws NoFileSpecifiedException, IOException {
        if (fileName != null) {
            writeFile(fileName);
        } else {
            throw new NoFileSpecifiedException();
        }
    }

    public void writeFile(String fileName) throws IOException {
        FileOutputStream out = new FileOutputStream(fileName);
        ObjectOutputStream objOut = new ObjectOutputStream(out);
        objOut.writeObject(preferences);
        objOut.flush();
    }

    public String get(String key) throws NoSuchFieldException {
        int index;
        try {
            index = getKeyIndex(key);
            String[] keyPair = preferences.get(index);
            return keyPair[1];
        } catch (NoSuchFieldException ex) {
            throw new NoSuchFieldException();
        }

    }

    public void set(String key, String value) {
        try {
            remove(key);
        } catch (NoSuchFieldException ex) {
            // no need to catch, if key does not exist then
            // continue and set the new key
            ;
        }
        String[] keyPair = {key, value};
        preferences.add(keyPair);
    }

    public void remove(String key) throws NoSuchFieldException {
        int keyIndex = getKeyIndex(key);
        preferences.remove(keyIndex);
    }

    private int getKeyIndex(String key) throws NoSuchFieldException {
        int index = -1;

        if (!preferences.isEmpty()) {
            for (int i = 0; i <= preferences.size()-1; i++) {
                String[] keyPair = preferences.get(i);
                if (keyPair[0]==key) { index = i; }
            }
        }

        if (index != -1) {
            return index;
        } else {
            throw new NoSuchFieldException();
        }
    }

    public void showDialog(boolean modal) {
     ;
    }
    
    public void showDialog() {
        showDialog(false);
    }
}