Just closing connection enough?

Question

Hi friends..This is my first post...I am a newbie Java Developer..Okay Here goes
I have just made a LAN based Java application using Swing,JDBC with backend as MS-Access..The backend is on a shared network drive..
The application is distributed as jar files on the LAN PCs..
Everywhere I have connected to the database I have just closed the connection explicitly like this
con.close();
I do not close the associated resultset and statement explicitly
The specification says associated statements and resultsets close when you close
the connection,even if you don't explicitly close them
Also I am not using connection pool..its simple basic connection using DriverManager
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String url = "jdbcdbcSN name";
String user = "";
String pw = "";
con = DriverManager.getConnection(url, user, pw);
Statement stmt = con.createStatement();
String select = "" ;
ResultSet rows = stmt.executeQuery(select);
Till now no performance problems..over 4K records have been added..
JVM is not exiting or anything..
On the net everyone says to explicitly close everything..but I did not know that
earlier..
My question is
Is closing just the connection enough..?
Is there any way I can check whether statements and resultsets have been implicitly closed?
Later on will it cause any performance problems or anything...?
Shud I change my code and add rs.close() and stmt.close() everywhere..?
If specification says everything closes on
closing connection why do ppl insist on closing everything explicitly..?
Or is this driver dependent..don't the drivers go through the specification..
My driver is the Sun JDBC ODBC bridge.....
There would be 8-10 users maximum at a time using the application concurrently...
Any help would be appreciated..Thanks in advance..

Answer 1

@jschell
Thanks for your help
I was running a few more tests..can you please explain the the following code...
Code
import java.sql.*;
import java.io.*;
class gc5test
public static void main(String args[])
Connection con = null;
long memoryBeforeSelects;
long memoryAfterSelects;
long memoryAfterConnectionClose;
try
PrintWriter pw= new PrintWriter("c:\\log1.txt");
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String url = "jdbc:odbc:pravahcon";
String user = "admin";
String pass = "ash123";
for(int i=1;i<=20;i++)
pw.println("Connection No"+i);
memoryBeforeSelects = Runtime.getRuntime().freeMemory();
pw.println("Free Memory before making connection " + memoryBeforeSelects / 1024 + " kB");
con = DriverManager.getConnection(url, user, pass);
Statement stmt = con.createStatement();
String select = "SELECT * FROM Users" ;
ResultSet rows = stmt.executeQuery(select);
memoryAfterSelects = Runtime.getRuntime().freeMemory();
pw.println("Free Memory after making connection " + memoryAfterSelects / 1024 + " kB");
rows.close();
stmt.close();
con.close();
memoryAfterConnectionClose = Runtime.getRuntime().freeMemory();
pw.println("Free Memory after closing connection " + memoryAfterConnectionClose / 1024 + " kB");
pw.close();
catch (ClassNotFoundException f)
System.out.println(f.getMessage());
System.exit(0);
catch (SQLException g)
System.out.println(g.getMessage());
System.exit(0);
catch (Exception e)
System.out.println(e.getMessage());
System.exit(0);
Output
Connection No1
Free Memory before making connection 4729 kB
Free Memory after making connection 4675 kB
Free Memory after closing connection 4675 kB
Connection No2
Free Memory before making connection 4675 kB
Free Memory after making connection 4638 kB
Free Memory after closing connection 4620 kB
Connection No3
Free Memory before making connection 4620 kB
Free Memory after making connection 4584 kB
Free Memory after closing connection 4584 kB
Connection No4
Free Memory before making connection 4584 kB
Free Memory after making connection 4548 kB
Free Memory after closing connection 4529 kB
Connection No5
Free Memory before making connection 4529 kB
Free Memory after making connection 4493 kB
Free Memory after closing connection 4493 kB
Connection No6
Free Memory before making connection 4493 kB
Free Memory after making connection 4457 kB
Free Memory after closing connection 4457 kB
Connection No7
Free Memory before making connection 4439 kB
Free Memory after making connection 4403 kB
Free Memory after closing connection 4403 kB
Connection No8
Free Memory before making connection 4403 kB
Free Memory after making connection 4367 kB
Free Memory after closing connection 4367 kB
Connection No9
Free Memory before making connection 4349 kB
Free Memory after making connection 4313 kB
Free Memory after closing connection 4313 kB
Connection No10
Free Memory before making connection 4313 kB
Free Memory after making connection 4277 kB
Free Memory after closing connection 4277 kB
Connection No11
Free Memory before making connection 4259 kB
Free Memory after making connection 4223 kB
Free Memory after closing connection 4223 kB
Connection No12
Free Memory before making connection 4223 kB
Free Memory after making connection 4187 kB
Free Memory after closing connection 4169 kB
Connection No13
Free Memory before making connection 4169 kB
Free Memory after making connection 4817 kB
Free Memory after closing connection 4800 kB
Connection No14
Free Memory before making connection 4800 kB
Free Memory after making connection 4766 kB
Free Memory after closing connection 4766 kB
Connection No15
Free Memory before making connection 4766 kB
Free Memory after making connection 4714 kB
Free Memory after closing connection 4714 kB
Connection No16
Free Memory before making connection 4714 kB
Free Memory after making connection 4678 kB
Free Memory after closing connection 4678 kB
Connection No17
Free Memory before making connection 4678 kB
Free Memory after making connection 4627 kB
Free Memory after closing connection 4627 kB
Connection No18
Free Memory before making connection 4627 kB
Free Memory after making connection 4592 kB
Free Memory after closing connection 4575 kB
Connection No19
Free Memory before making connection 4575 kB
Free Memory after making connection 4540 kB
Free Memory after closing connection 4540 kB
Connection No20
Free Memory before making connection 4540 kB
Free Memory after making connection 4489 kB
Free Memory after closing connection 4489 kB
The memory is not being freed immediately after closing connection explicitly in first 12 iterations..
In the first 12 iterations memory after making connection and memory after closing
connection are the same/or very less difference...
Only in the 13th iteration the memory increases from 4169 to 4817..
Why is this happening..?
I am closing everything explicitly..
Shouldn't the memory be reclaimed immediately..?
Insted it is happening later on..
Am I missing something here..?