/**
 * Keeps track of each sentence that has been sent and
 * can return the 10 sentences that have been used most often.
 */
public interface TopTen {

    /**
     * Records that the sentence has been sent.
     * @param sentence the sentence sent, ignored if null
     */
    public void recordSentenceSent(String sentence);

    /**
     * @returns an array of length 10 with the sentences
     * ordered from most frequent to least frequent
     * If fewer than 10 phrases have been used, the empty
     * spaces in the array are null
     * If two sentences have the same frequency, then the one
     * that was used more recently is listed first.
     */
    public String[] getTopTen();

}