Help with Maps

[snripa]

I need help with maps (Thinking inJava 3-d ed., 11#34).
I have my class:

public class SlowMap extends AbstractMap {
  //private static Test monitor = new Test();
  private List
    keys = new ArrayList(),
    values = new ArrayList();
    @Override
  public Object put(Object key, Object value) {
    Object result = get(key);
    if(!keys.contains(key)) {
      keys.add(key);
      values.add(value);
    } else
      values.set(keys.indexOf(key), value);
    return result;
  }
    @Override
  public Object get(Object key) {
    if(!keys.contains(key))
      return null;
    return values.get(keys.indexOf(key));
  }
  public Set entrySet() {
    Set entries = new HashSet();
    Iterator
      ki = keys.iterator(),
      vi = values.iterator();
    while(ki.hasNext())
      entries.add(new MPair(ki.next(), vi.next()));
    return entries;
  }
    @Override
  public String toString() {
    StringBuffer s = new StringBuffer("{");
    Iterator
      ki = keys.iterator(),
      vi = values.iterator();
    while(ki.hasNext()) {
      s.append(ki.next() + "=" + vi.next());
      if(ki.hasNext()) s.append(", ");
    }
    s.append("}");
    return s.toString();
  }
  public static void main(String[] args) {
    SlowMap m = new SlowMap();
    Collections2.fill(m, Collections2.geography, 15);
    System.out.println(m);

  }
}

It doesn't work when i want to delete smth or deleteAll. (There are no errors but nothing happens when I use map.clear)
How should I modify this?

[pbrockway2]

If you're making a modifiable map the API docs say that "the iterator returned by entrySet().iterator() must additionally implement its remove method". The iterator of the set returned by entrySet() does implement remove(): but that implementation isn't actually removing anything from the map.

[Edit]

How should I modify this?

This is just a guess, but perhaps the set returned by entrySet() could be an inner class whose iterator() returns an iterator where remove() alters the map. (If it's not considered "cheating" I would have a look at src.zip.)

[pbrockway2]

In fact the API docs for entrySet() should be studied because by returning a new HashSet you are not fulfilling the contract that "changes to the map are reflected in the set, and vice-versa".

Perhaps there's more to this: including what an MPair is.

[snripa]

That's MPair

public class MPair implements Map.Entry, Comparable {
  private Object key, value;
  public MPair(Object k, Object v) {
    key = k;
    value = v;
  }
  public Object getKey() { return key; }
  public Object getValue() { return value; }
  public Object setValue(Object v) {
    Object result = value;
    value = v;
    return result;
  }
  public boolean equals(Object o) {
    return key.equals(((MPair)o).key);
  }
    public int hashCode() {
        int hash = 7;
        hash = 17 * hash + (this.key != null ? this.key.hashCode() : 0);
        return hash;
    }
  public int compareTo(Object rv) {
    return ((Comparable)key).compareTo(((MPair)rv).key);
  }
}

[snripa]

I added clear() method to SlowMap

@Override
    public void clear(){
    keys.clear();
    values.clear();
    }

it works, when i call map.clear but when I do operations with set it still doesn't work

I understand I should additionly implement remove() method for entrySet.iterator, but have no idea where to do that...