Server Administration :: How To Get Number Of Empty Block

①SQL> SELECT OBJECT_ID FROM DBA_OBJECTS WHERE OBJECT_NAME='T2012';
OBJECT_ID
---------
57082

②SQL> SELECT HEADER_BLOCK,BLOCKS FROM DBA_SEGMENTS WHERE SEGMENT_NAME = 'T2012';
HEADER_BLOCK BLOCKS
------------- --------
683 8

③SQL> SELECT DBMS_ROWID.rowid_block_number(ROWID)USED_BLOCK_NUMBER FROM SCOTT.T2012;
USED_BLOCK_NUMBER
----------------
684

④SQL> SHUTDOWN IMMEDIATE;

⑤SQL> STARTUP;

⑥SQL> SELECT BLOCK#,CLASS# FROM V$BH WHERE OBJD = '57082';
no data found

⑦SQL> SELECT * FROM SCOTT.T2012;
ID
-----
1

⑧SQL> SELECT BLOCK#,CLASS# FROM V$BH WHERE OBJD='57082';
BLOCK# CLASS#
------- ----------
686 1
684 1
687 1
685 1
688 1
683 4

⑨SQL> SELECT EMPTY_BLOCKS FROM DBA_TABLES WHERE TABLE_NAME='T2012';
EMPTY_BLOCKS
------------
3

QUESTIONS ONE:
in the ⑧ step,why block#685,block#686,block#687,block#688 in the buffer cache after i query data from scott.T2012?

QUESTIONS TWO:
in the ⑨ step,what's the block number of the empty block?just like DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID).