var square:Sprite = new Sprite();

addChild(square);
square.graphics.lineStyle(3,0x00ff00);
square.graphics.beginFill(0x0000FF);
square.graphics.drawRect(0,0,100,100);
square.graphics.endFill();
square.x = stage.stageWidth/2-square.width/2;
square.y = stage.stageHeight/2-square.height/2;