How to avoid overlapping groups after expanding a group

when we arrange two table vertically and expand the upper table then table which present at bottom get overlapped by upper table. @walter can you help us.

The general answer is that the container’s layout is responsible.

See for example the Swimlanes sample, Swim Lanes. It defines a PoolLayout, which is basically a customized GridLayout. The Diagram.layout is a PoolLayout that arranges all of the pools so that they do not overlap each other. The Group.layout for each “Pool” group is also a PoolLayout, which is responsible for making sure the lanes are the same length and not overlapping, even while the user is resizing a lane.

I do not know how you want to layout your diagram, but ultimately you should either use an existing Layout to position the groups so that they do not overlap each other, or else you will need to implement a custom Layout to achieve your requirements.