ResultSet的gtter方法只能读取一次，为何如此设计？

Question

java.sql.ResultSet接口的API里这样写的:

 * The <code>ResultSet</code> interface provides
 * <i>getter</i> methods (<code>getBoolean</code>, <code>getLong</code>, and so on)
 * for retrieving column values from the current row.
 * Values can be retrieved using either the index number of the
 * column or the name of the column.  In general, using the
 * column index will be more efficient.  Columns are numbered from 1.
 * For maximum portability, result set columns within each row should be
 * read in left-to-right order, and each column should be read only once.

还是不理解为什么要设置成getter方法只能读取一次。