Exception in thread "main" java.lang.NullPointerException

[SoooConfused]

I haven't been using java that long, but I'm currently in a class and we've been given this program to complete; I have been working on this for the last for 3 days now and I keep getting this error:

Selecting the correct constructor
Exception in thread "main" java.lang.NullPointerException
at SlotReservation.main(SlotReservation.java:80)

referenced code:

while(answer<1750)
{
answer++;
//Selecting a user randomly from the user table such that he is not in the parking lot and has not been used till now.

ResultSet rs1=stmt.executeQuery("SELECT MIN(car_regnum), start_time,end_time FROM fsbm_data where temp_present='0' and temp_block='0'");
if (rs1.next())
{
arrivalThreadRegnum = Integer.parseInt(rs1.getString(1).trim());
startTime = Integer.parseInt(rs1.getString(2).trim());
endTime = Integer.parseInt(rs1.getString(3).trim());
stmt.executeUpdate("UPDATE fsbm_data set temp_present=1, temp_block=1 where car_regnum="+rs1.getString(1));

//Calling thread for each new user and sending his registration number and advance reservation spot number

new FreeSpaceDetection(userPL.summaryVector,userPL.bit Map,arrivalThreadRegnum, startTime,endTime,userPL.defragList);

slotNumber++;
try
{
Thread.sleep(1000);
}
END OF MY CODE:

I typed everything as it was presented, but I can't get it to run without this error.
Any suggestions would be much appreciated...

[KevinWorkman]

Something on that line is null. What is it? Use a debugger or some print statements to figure that out.

[SoooConfused]

Thanks for those words

I have tried debugging, and it found nothing.

this is the entire page of code:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Vector;

public class SlotReservation {

Vector<Integer> summaryVector = new Vector<Integer>();
ArrayList<slotInfo> defragList = new ArrayList<slotInfo>();
int[][] bitMap=new int [48][500];


public static void main (String args [])
{

SlotReservation userPL = new SlotReservation();
userPL.summaryVector = new Vector<Integer>();
userPL.defragList = new ArrayList<slotInfo>();
int answerLimit = 0;
//Arrival Thread Variable initialization

int slotNumber = 0;
int startTime = 0;
int endTime = 0;
int arrivalThreadRegnum = 0;

//Setting up database connection

Connection conn = null;

try
{

String userName = "root";
String password = "";
String url = "jdbc:mysql://localhost/mysql";
Class.forName ("com.mysql.jdbc.Driver").newInstance ();
conn = DriverManager.getConnection (url, userName, password);
}
catch (Exception e)
{
System.err.println ("Cannot connect to database server");
}
finally
{
if (conn != null)
{
Statement stmt = null;
int answer=1;
try
{
stmt = conn.createStatement();
ResultSet rs=stmt.executeQuery("SELECT MIN(car_regnum), start_time,end_time FROM fsbm_data where temp_present='0' and temp_block='0'");
if (rs.next())
{
System.out.println("Selecting the correct constructor");
new DefragmentAllocations3(userPL);
//new DefragmentAllocations2(userPL);
//new DefragmentAllocations3(userPL);
}


while(answer<1750)
{
answer++;
//Selecting a user randomly from the user table such that he is not in the parking lot and has not been used till now.

ResultSet rs1=stmt.executeQuery("SELECT MIN(car_regnum), start_time,end_time FROM fsbm_data where temp_present='0' and temp_block='0'");
if (rs1.next())
{

arrivalThreadRegnum = Integer.parseInt(rs1.getString(1).trim());
startTime = Integer.parseInt(rs1.getString(2).trim());
endTime = Integer.parseInt(rs1.getString(3).trim());
stmt.executeUpdate("UPDATE fsbm_data set temp_present=1, temp_block=1 where car_regnum="+rs1.getString(1));

//Calling thread for each new user and sending his registration number and advance reservation spot number

new FreeSpaceDetection(userPL.summaryVector,userPL.bit Map,arrivalThreadRegnum, startTime,endTime,userPL.defragList);
slotNumber++;
try
{
Thread.sleep(1000);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
else
System.out.println("No more users available to simulate the arrival threads");
}
}
catch (SQLException e1)
{
e1.printStackTrace();
}

}
}
System.out.println("DEFRAG LIST AT END OF MAIN IS "+userPL.defragList);

}

}


Complete page of code... Error Still occurring after running debugger...

[KevinWorkman]

When posting code, please use the highlight tags to preserve formatting. Unformatted code is pretty hard to read.

A debugger doesn't find or fix anything for you. It simply allows you to examine the values while the code is running. I'd add a break point right before the line that errors, run the debugger, and examine each variable- one of them is null. Alternatively you could use a print statement, like so: http://www.javaprogrammingforums.com...t-println.html