function AnimationClass( dir, pictures, pictureID, times2show, speed )
    {   // AnimationClass
        this._dir = dir;
        this._pictures = pictures;
        this._pictureID = pictureID;
        this._times2show = times2show;
        this._speed = speed;
        this._intID = 0;
        this._count = 0;

        // show the first picture
        this.ChangePicture( );
    }   // AnimationClass

    AnimationClass.prototype.StartAnimation = function( )
    {   // StartAnimation
        var instant = this;

        this._intID = setInterval( function( ) { instant.ChangePicture( ); }, this._speed );
    }   // StartAnimation

    AnimationClass.prototype.ChangePicture = function( )
    {   // ChangePicture
        var     whichPicture = Math.random( );
        var     len = this._pictures.length;
        var     pictureID = document.getElementById( this._pictureID );

        var     whichPicture2 = whichPicture * len;
        var     whichPicture3 = Math.floor( whichPicture2 );

        pictureID.src = this._dir + this._pictures[ whichPicture3 ];

        if ( this._times2show > 0 && this._times2show <= ++this._count )
        {
            clearInterval( this._intID );
        }
    }   // ChangePicture