Why : Exception in thread

Question

Hi guys again it's me;
Rushing up for a project is really not good(especially for a beginner). I have this program which indicates a person's travel diary randomly. the program that I write should indicate normally;
House : frequence 2
SportsCentre : frequence 3
and so on...
The problem is there is a
Exception in thread "main" java.lang.NullPointerException
everytime I execute it. Only some random times, it gets to show a line or two.
I blinded sitting in front of the comp for so long, so I'm really hoping someone could explain the error to me. Here are the codes;
import java.util.Random;
Deplacement class
public class Deplacement
     /**listing of all the places the cadre(executive) can go
     private final int location;
          public final static int house   = 1;
          public final static int company = 2;
          public final static int sportscentre = 3;
          public final static int restaurant  = 4;
          public final static int restouniv  = 5;
          public final static int ASSEDIC   = 6;
          public final static int school = 7;
     public Deplacement(int location, int freq)
             assert isValidLocation(location);
             this.location = location;
     public int getLocation()
        return location;
     public static int getRandom(int start, int end) //generates random between 2 numbers
          Random f = new Random();
          int frequence = f.nextInt(end - start + 1) + start;
          return frequence;
     public static boolean isValidLocation(int location) {
        return house <= location && location <= school;
     public static String locationToString(int location)
              switch (location)
              case house: return "House";
              case company: return "Company";
              case sportscentre: return "Sports Centre";
              case restaurant: return "Restaurant";
              case restouniv: return "Resto-U";
              case ASSEDIC: return "ASSEDIC";
              case school: return "School";
               return null;
         }Table class
public class Table
     public static int numLocation = 7;
    public static int numFrequence = 11;
    private Deplacement[][] table;
    public Table()
        table = new Deplacement[numLocation][numFrequence];
        for (int location = Deplacement.house;
             location <= Deplacement.school; location++)
           int frequence = 1;
           table [location-1][Deplacement.getRandom(0, 10)] = new Deplacement(location, frequence);
    public Deplacement getDeplacement(int location, int frequence)
        return table [location-1][frequence];
}Simulate class
public class Simulate
     private static final int frequence = 0;
     public static void main(String[] args)
        Table table = new Table();
        for (int location = Deplacement.house; location <= Deplacement.school; location++)
                Deplacement simulate = table.getDeplacement(location, frequence);
                System.out.printf("%s : fr�quence %d \n", simulate.locationToString(simulate.getLocation()),(simulate.getRandom(0, 10)));  // <--exception is generated here
}Really hoping you guys could paste this in, and tell me voila here the error. I don't understand why the exception is generated. Been looking at it for 2hours. Please help.

Answer 1

System.out.printf("%s : fr�quence %d \n",simulate.locationToString(simulate.getLocation()),(sim
ulate.getRandom(0, 10))); // <--exception is
generated here
Ok, so simulate is null, and you're trying to invoke
methods(locationToString, getLocation, and getRandom)
on a null object reference, which is illegal of
course.
Deplacement simulate =table.getDeplacement(location, frequence);
getDeplacement must sometimes return null depending
on what data you pass it. Check it!
if (simulate == null)
System.out.println("OOPS! I'd better fix this!");
else
System.out.println("%s : fr�quence .........
}I took care of the exception in Class Simulate. SO it looks like this.
public class Simulate
     private static final int frequence = 0;
     public static void main(String[] args)
        Table table = new Table();
        for (int location = Deplacement.house; location <= Deplacement.school; location++)
               try
                    Deplacement simulate = table.getDeplacement(location, frequence);
                   System.out.printf("%s : fr�quence %d \n",
                             simulate.locationToString(simulate.getLocation()),(simulate.getRandom(0, 10)));
               catch (java.lang.NullPointerException npe)
                    System.out.println("WHY");
    }Sample results...
WHY
WHY
Sports Centre : fr�quence 4
WHY
WHY
WHY
WHY
I'm sorry, but I might not get the idea. How can getDeplacement(location, frequence) egals null when I actually have all the locations from 1-7(house to school) and a frequence that can take only int from 0-10? I suspect the random method that returned a null frequence but how is that possible? Can anybody help? Thank you.