A Map implemented with ArrayLists

[Java Tip]

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

public class SlowMap extends AbstractMap {

  private List keys = new ArrayList(), values = new ArrayList();

  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;
  }

  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;
  }

  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();
    m.put("Adobe", "Mountain View, CA");
    m.put("IBM", "White Plains, NY");
    m.put("Learning Tree", "Los Angeles, CA");
    m.put("Microsoft", "Redmond, WA");
    m.put("Netscape", "Mountain View, CA");
    m.put("O'Reilly", "Sebastopol, CA");
    m.put("Sun", "Mountain View, CA");
    System.out.println(m);

  }
} 

class MPair implements Entry, Comparable {
  Object key, value;
  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 compareTo(Object rv) {
    return ((Comparable)key).compareTo(
      ((MPair)rv).key);
  }
}