Face problem in "tetris game"

Hi to all;

I try to program " tetris game "

First i did the point about :

Cube Block falling to the floor and another one appear then falling also but my problem is whe cube block fall and there is another one the floor the falling mix with the one on the floor !!!

Although i make a conditon that prevent mixing.

from here      http://www.mediafire.com/?khg2p2mlpxpixz6    you can download my code .

There is there package in package TetrisView There is class TetrisCell which have the problem in method moveBlockVerticle()(); 

you will fin dthis code in it for prevent mixing bloks :

 if (tetrisBlockShapesEnum == tetrisBlockShapesEnum.CUBE_BLOCK && nextRow - 2 == blockData.getPoint().getX()
                            || tetrisBlockShapesEnum == tetrisBlockShapesEnum.I_BOLCK && nextRow - 4 == blockData.getPoint().getX()) {
                        canDraw = false;
                    } else {
                        canDraw = true;
                    }

but also the cude block mix !!!!

why this !!!

I hope to help me

thanks in advnce