Moves the cursor forward one row from its current position. A ResultSet cursor is initially positioned before the first row; the first call to the method next makes the first row the current row; the second call makes the second row the current row, and so on.
When a call to the next method returns false, the cursor is positioned after the last row. Any invocation of a ResultSet method which requires a current row will result in a SQLException being thrown. If the result set type is TYPE_FORWARD_ONLY, it is vendor specified whether their JDBC driver implementation will return false or throw an SQLException on a subsequent call to next.

If an input stream is open for the current row, a call to the method next will implicitly close it. A ResultSet object's warning chain is cleared when a new row is read.

true if the new current row is valid; false if there are no more rows
SQLException - if a database access error occurs or this method is called on a closed result set

即执行Java sql语句得到一个resultset之后。直接去获取结果集的内容是无法获取到数据的。因为一个结果集的光标是停留在第一行前面的。你要处理第一行的数据,就首先,将光标移动到第一行。如果光标已经超出有效行数,会报SQLException