This section describes what is ResultSet cursor and ResultSet scrollability.
Each ResultSet object maintains a cursor (pointer) to identify the current data row.
The cursor of a newly created ResultSet object is positioned before the first row.
How to move the cursor is depending on the scrollability of the ResultSet.
1. Non-scrollable ResultSet - The ResultSet object type is ResultSet.TYPE_FORWARD_ONLY, the default type. Non-scrollable ResultSet supports
only cursor move method:
next() - Moves the cursor forward one row from its current position.
2. Scrollable ResultSet - The ResultSet object type is ResultSet.TYPE_SCROLL_INSENSITIVE, or ResultSet.TYPE_SCROLL_SENSITIVE.
Scrollable ResultSet supports a number of cursor move methods:
first() - Moves the cursor to the first row in this ResultSet object.
last() - Moves the cursor to the last row in this ResultSet object.
next() - Moves the cursor forward one row from its current position.
previous() - Moves the cursor backward one row from its current position.
absolute(+/-n) - Moves the cursor to the given row number in this ResultSet object. Negative row number counts backward from the last row.
relative(+/-n) -Moves the cursor a relative number of rows, either positive or negative.
Attempting to move beyond the first/last row in the result set positions the cursor before/after the first/last row.
Calling relative(0) is valid, but does not change the cursor position.
Here is a sample program that loops through the ResultSet rows forward only with next() method:
/**
* DerbyLoopResultSet.java
* Copyright (c) 2007 by Dr. Herong Yang. All rights reserved.
*/
import java.sql.*;
public class DerbyLoopResultSet {
public static void main(String [] args) {
Connection con = null;
try {
con = DriverManager.getConnection(
"jdbc:derby://localhost/TestDB");
Statement sta = con.createStatement();
// Catch the ResultSet object
ResultSet res = sta.executeQuery("SELECT * FROM Profile");
// Check ResultSet's scrollability
if (res.getType() == ResultSet.TYPE_FORWARD_ONLY) {
System.out.println("ResultSet non-scrollable.");
} else {
System.out.println("ResultSet scrollable.");
}
// Move cursor forward only with next()
System.out.println("List of Profiles:");
while (res.next()) {
String firstName = res.getString("FirstName");
String lastName = res.getString("LastName");
System.out.println(" "+firstName+" "+lastName);
}
// Close ResultSet
res.close();
sta.close();
con.close();
} catch (Exception e) {
System.err.println("Exception: "+e.getMessage());
}
}
}
The output is listed below:
ResultSet non-scrollable.
List of Profiles:
Janet Gates
21d6 efd17
1002 e3873
11bd 58ad0
1352 17d9
13ba 88356
1090 3fb07
19c2 8770b
Keith Harris
