Null pointer not found exception

Question

Hi,
I keep getting the error mentioned in the subject heading, through the use of this code:
// set relevant to false
               relevant = false;
               // if there are two data slots, it is worthwhile to sort them
               if (counter > 1) relevant = true;
               // do the following if relevant is true
               if (relevant = true)
                   // set all the variables needed for this sort.
                   String[] names = new String[10];
                   AirlineTicket[] temp = new AirlineTicket[10];
                   int[] indexes = new int[10];
                   int tmp;
                   // do the selection sort on names only
                   for (int j = 0; j < data.length; j++)
                       names[j] = getNames(data[j]);
                       for (int i = 0; i < data.length; i++) System.out.println(names);
selectionSort(names);
// match names to the data array and record index position
for (int j = 0; j < data.length; j++)
tmp = matchNames(names, data[j]);
indexes[j] = tmp;
// put the data at indexes[j] in the sorting place in temp
for (int j = 0; j < data.length; j++)
if (indexes[j] != -1)
data[indexes[j]] = temp[j];
// move back from temp to data - now sorted
for (int j = 0; j < data.length; j++)
data[j] = temp[j];
// let the user know what's happened
System.out.println("The data is now sorted.");
Above is the main method of the program. Below are the methods it refers to:
   // match names against the data array's names and report index number
   public static int matchNames(String[] names, AirlineTicket in)
       // set variables
       String name;
       int index = 0;
       // select one name to test
       name = in.getName();
       // cycle through array
       for (int j = 0; j < names.length; j++)
           // if the name is matched and not null, index = j, or return -1
           if (names[j] == name && name  != null && names[j] != "a") index = j;
           else  index = -1;
       return index;
   // smallest(): find the 'smallest' string in a range
   public static int smallest (String[] array, int start, int finish)
      // assume the first item is the smallest
      int lowest = start;
      // scan the rest of the array segment for anything smaller
      // and re-set the recorded lowest if necessary
      for(int i = start + 1; i < finish; i++)
         if (array.compareTo(array[lowest]) < 0)
lowest = i;
// return the lowest index
return lowest;
// swap(): swap one element with another
public static void swap(String[] data, int a, int b)
String temp = data[a];
data[a] = data;
data[b] = temp;
// selectionSort(): sort a string array
public static void selectionSort(String[] data)
// cycle through the array (except for the last element)
for (int index = 0; index < data.length - 1; index++)
// find the smallest in the remaining section
int small = smallest(data, index, data.length);
// swap current position with smallest
swap(data, index, small);
Now, the error it gives me is this (during runtime):
Exception in thread "main" java.lang.NullPointerException
at TicketManager.smallest(TicketManager2.java:349)
at TicketManager.selectionSort(TicketManager2.java:371)
at TicketManager.main(TicketManager2.java:270)
What do you think would be causing the problem? I did my best to get rid of the nulls, and tried put a System.out.println(); line just before it tells it to selectionSort(names); to see what it prints. It prints the first line of what it should, and from then on, nothing but null. I don't think the matchNames method is actually doing its job properly. Any ideas?
Regards,
Platinum

Answer 1

// put the data at indexes[j] in the sorting place in temp
for (int j = 0; j < data.length; j++)
if (indexes[j] != -1)
data[indexes[j]] = temp[j];
}try swapping this over.temp[j] = data[indexes[j]];It seems you just want to sort data[], if this is the case, then use:public class AirlineTicket implements Comparable
  // all your AirlineTicket code
  // goes here
  public int compareTo(Object obj)
    AirlineTicket at = (AirlineTicket)obj;
    return this.getName().compareTo(at.getName());
}Then you can just use Arrays.sort(data);