/**
 * Very simple dictionaries that map keys to values.
 *
 * @author Samuel A. Rebelsky
 * @version 1.2 of April 2000
 */
public interface Dictionary {
    /**
     * Add an entry to the dictionary.
     * Pre: The key and value are non-null.
     * Pre: The key can be compared to other values in the dictionary.
     * Post: Subsequent calls to get(key) will return value.
     *
     * @exception Exception
     *   If the key cannot be compared.
     */
    public void add(Object key, Object value)
          throws Exception;

    /**
     * Determine if a particular key is in the dictionary.
     * Pre: None.
     * Post: Returns true if the key is in the dictionary;
     *       Returns false otherwise.
     */
    public boolean contains(Object key);

    /**
     * Delete an entry in the dictionary.
     * Pre: The key is non-null.
     * Pre: The key can be compared to other values in the dictionary.
     * Post: Deletes the entry.
     * Note: Added in version 1.2.

     * @exception Exception
     *   If the key cannot be compared or there is no such entry.
     */
    public void delete(Object key)
          throws Exception;

    /**
     * Look up an entry in the dictionary.
     * Pre: The key is non-null.
     * Pre: The key can be compared to other values in the dictionary.
     * Post: Returns the value most recently "put" with the key.  
     *
     * @exception Exception
     *   If the key cannot be compared or there is no such entry.
     */
    public Object lookup(Object key)
          throws Exception;

} // interface Dictionary