// postcondition: returns the number of words in this WordList that
  //                are exactly len letters long
  public int numWordsOfLength(int len)
  {
    int count = 0;

    for (int i = 0; i < myList.size(); i++)
      if (((String)myList.get(i)).length() == len) 1
        count++;

    return count;
  }

1. The cast to String is necessary to call its length method.

  // postcondition: all words that are exactly len letters long
  //                have been removed from this WordList, with the
  //                order of the remaining words unchanged
  public void removeWordsOfLength(int len)
  {
    int i = 0;

    while (i < myList.size()) 1
    {
      if (((String)myList.get(i)).length() == len)
        myList.remove(i); 2
      else
        i++;
    }
  } 3

1. A while loop is more convenient for a traversal with removals than a for loop.
   
   
2. When we remove a value, myList.size() is decremented and the indices of the subsequent values are decremented by one.  In that case, we don't increment i.
   
   
3. A solution with an iterator is acceptable, too, and it is actually shorter and safer:

     public void removeWordsOfLength(int len)
     {
       Iterator iter = myList.iterator();
   
       while (iter.hasNext())
       {
         if (((String)iter.next()).length() == len)
           iter.remove();
       }
     }