select * from recyclebin;

using this query we can see the tables which are dropped. its applicable only in oracle 10g.

You can use this command to retrieve the dropped table simply by querying
FLASHBACK TABLE <table_name> TO BEFORE DROP;

you can also query this to view the objects that can be undropped
SHOW RECYCLEBIN

When you drop a table normally the database does not immediately release the space associated with the table. Rather the database renames the table and places it in a recycle bin where it can later be recovered with the FLASHBACK TABLE statement if you find that you dropped the table in error.

FLASHBACK TABLE RECYCLETEST TO BEFORE DROP;