public boolean containsKey(Comparable key) {
        return this.store.containsKey(key);
    }
    
    /**
     * Adds a mapping between the specified <code>key</code> and 
     * <code>paint</code> values.
     * 
     * @param key  the key (<code>null</code> not permitted).
     * @param paint  the paint.
     * 
     * @throws IllegalArgumentException if <code>key</code> is 
     *     <code>null</code>.
     */
    public void put(Comparable key, Paint paint) {
        if (key == null) {
            throw new IllegalArgumentException("Null 'key' argument.");
        }
        this.store.put(key, paint);
    }
    
    /**
     * Resets the map to empty.
     */
    public void clear() {
        this.store.clear();