Reusing free space in a table

Hi:

I have a tablespace of 5 Gbytes. It has 10 datafiles of 500 Mbytes ( No autoextend ). I have 1 table of 4.5 Gbytes. This table has a lot of extends. I have deleted 1 Gbyte of this table but Oracle seems not to reuse this space.

Is this 'normal' in Oracle ?
Why ?
Is there any command to reallocate free space of deleted rows ?

Note: I want to avoid the classic way... ( I have 3.5 Gbytes in the table ! )

1. Export data
2. Drop table
3. Create table
4. Import data