please help getting java.lang.nullpointerexception while running the program

please help getting java.lang.nullpointerexception while running the program

help me out with this code,i am getting run time exception error
java.lang.nullpointerexception plz help me solving this and how to access
any file on desktop using java program , like i want to access any image
or text file on desktop or in any other folde what code should i write
.FYI i am noob.
import java.io.*;
class jarvis
{
public static void main(String args[])
{
String i=null,j=null,k=null,l=null,m=null,n=null,o=null,a=null,q=null;
try
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Command me: ");
if(i.equals("jarvis you there?"))
{
i=br.readLine();
System.out.println("at your service sir");
}
System.out.println("Command me: ");
if(j.equals("run command prompt"))
{
j=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("cmd.exe /c start");
}
System.out.println("Command me: ");
if(k.equals("run notepad"))
{
k=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("notepd.exe");
}
System.out.println("Command me: ");
if(l.equals("run paint"))
{
l=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("mspaint.exe");
}
System.out.println("Command me: ");
if(m.equals("open facebook"))
{
m=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("cmd.exe /c start www.facebook.com");
}
System.out.println("Command me: ");
if(n.equals("open google"))
{
n=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("cmd.exe /c start www.google.com");
}
System.out.println("Command me: ");
if(o.equals("open youtube"))
{
o=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("cmd.exe /c start www.youtube.com");
}
System.out.println("Command me: ");
if(a.equals("open yahoo"))
{
a=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("cmd.exe /c start www.yahoo.com");
}
System.out.println("Command me: ");
if(q.equals("open omegle"))
{
q=br.readLine();
Runtime r=Runtime.getRuntime();
Process p=r.exec("cmd.exe /c start www.omegle.com");
}
}
catch(Exception e)
{
System.out.print(e);
}
}
}