You are probably moving both horizontally and vertically at the same time -- using something like 'setLocation(getX()+dx, getY()+dy)'. By doing so, any collision cannot be easily determined from where (which direction of movement caused the collision). Separate the horizontal movement from the vertical movement and perform collision checking with each individually. For an example, look at my Jump and Run Demo w/Moving Platform demo. Just run it on the site and click the 'Who' button along the bottom of the window. The 'up' and 'down' keys will scroll the text as well as dragging the handle of the scrollbar along the right edge.