// collection of phone entries

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

public class PhoneBook implements Serializable
{
   protected LinkedList<PhoneEntry> entries = new LinkedList<PhoneEntry>();

   public boolean contains(String target_name)
   {
      return lookupEntry(target_name) != null;
   }

   public PhoneEntry lookupEntry(String target_name)
   {
      ListIterator<PhoneEntry> it = entries.listIterator();
      while ( it.hasNext() )
      {
         PhoneEntry next_entry = it.next();
         if ( next_entry.getName().equalsIgnoreCase(target_name) )
            return next_entry;
      }
      return null;
   }

   public String lookupNumber(String target_name)
   {
      PhoneEntry ent = lookupEntry(target_name);
      if ( ent == null )
         return null;
      else
         return ent.getNumber();
   }
   
   public void addEntry(PhoneEntry ent)
   {
      entries.add(ent);
   }

   public void addEntry(String name, String number)
   {
      addEntry(new PhoneEntry(name, number));
   }

   public void changeEntry(String name, String number)
   {
      PhoneEntry ent = lookupEntry(name);
      assert ent != null;
      ent.setNumber(number);
   }

}