using selection sort on 2 string arrays

[augiechimpo]

here is my code, for a selection sort on 2 string arrays returning nothing. i have 2 string arrays loaded from a file now i need to sort them. but everytime i run this i get a null pointer exception

public static void selectionSort(String[] array1, String[] array2)
{


int startScan, index, minIndex;
String minValue1, minValue2;

for (startScan = 0; startScan < (array1.length-1); startScan++)
{
minIndex = startScan;
minValue1 = array1[startScan];
minValue2 = array2[startScan];
for(index = startScan + 1; index < array1.length; index++)
{
if (array1[index].compareTo(minValue1) < 0)

{
minValue1 = array1[index];
minValue2 = array2[index];
minIndex = index;
}
}
array1[minIndex] = array1[startScan];
array2[minIndex] = array2[startScan];
array1[startScan] = minValue1;
array2[startScan] = minValue2;
}
}
can anyone please help me

here is my code to call from a file and load the array then attempt to sort and print out the result of the sort

public CommissionReport() throws IOException
{

Scanner keyboard = new Scanner(System.in);

System.out.print("Enter the file name: ");
String inputtedFileName = keyboard.nextLine();

File fileName = new File(inputtedFileName);

if(fileName.exists())
{
Scanner inputFile = new Scanner(fileName);

while(inputFile.hasNext())
{
for (int index = 0; index < ARRAY_SIZE; index++)
{
salesId[index] = inputFile.nextLine();


salesName[index] = inputFile.nextLine();

inputFile.close();





System.out.println(salesId[index]);
System.out.println(salesName[index]);

}

MyArrays.selectionSort(salesId, salesName);

}


}
else
{
System.out.println("File does not exist");
}

[pbrockway2]

everytime i run this i get a null pointer exception

A couple of things: first, when you post code, use the code tags. You put [code] at the start of your code and [/code] at the end. That way the indentation is preserved and the code remains readable.

Secondly if you get a runtime exception like a NullPointerException it is a good idea to copy and post the entire error message. It will refer to a line number in your code and you should say which line that is.

[augiechimpo]

public static void selectionSort(String[] array1, String[] array2) 
    {
       
   
      int startScan, index, minIndex; 
      String minValue1, minValue2;

      for (startScan = 0; startScan < (array1.length-1); startScan++)
      {
         minIndex = startScan;
         minValue1 = array1[startScan];
         minValue2 = array2[startScan];
         for(index = startScan + 1; index < array1.length; index++)
         {
            [B][U]if (array1[index].compareTo(minValue1) < 0)[/U][/B]
            
            {
               minValue1 = array1[index];
               minValue2 = array2[index];
               minIndex = index;
            }
         }
         array1[minIndex] = array1[startScan];
         array2[minIndex] = array2[startScan];
         array1[startScan] = minValue1;
         array2[startScan] = minValue2;
      }
   }

here is the other code again

public CommissionReport() throws IOException 
    {
        
        Scanner keyboard = new Scanner(System.in);
        
        System.out.print("Enter the file name: ");
        String inputtedFileName = keyboard.nextLine();
       
        File fileName = new File(inputtedFileName);
        
       if(fileName.exists())
       {
         Scanner inputFile = new Scanner(fileName);
        
         while(inputFile.hasNext())
         {
            for (int index  = 0; index < ARRAY_SIZE; index++)
            {
                salesId[index] = inputFile.nextLine();
               
            
                salesName[index] = inputFile.nextLine();
                
                inputFile.close();
                
                
                
                
         
                System.out.println(salesId[index]);
                System.out.println(salesName[index]);
                
            }
            
            MyArrays.selectionSort(salesId, salesName);
            
         }
         
         
       }
       else
       {
         System.out.println("File does not exist");
       }

here is the runtime error i get and the highlighted area

java.lang.nullpointerexception : null

the highlighted code is

if (array1[index].compareTo(minValue1) < 0)

[pbrockway2]

It looks like array1[index] is null. You can verify this by using System.out.println().

public static void selectionSort(String[] array1, String[] array2) 
{
   int startScan, index, minIndex; 
   String minValue1, minValue2;

   for (startScan = 0; startScan < (array1.length-1); startScan++)
   {
      minIndex = startScan;
      minValue1 = array1[startScan];
      minValue2 = array2[startScan];
      for(index = startScan + 1; index < array1.length; index++)
      {
         [color=blue]if(array1[index] == null)
         {
            System.out.println("array1 is null at index=" + index);
         }[/color]
         if (array1[index].compareTo(minValue1) < 0)
            
            {
               minValue1 = array1[index];
               minValue2 = array2[index];
               minIndex = index;
            }
         }
         array1[minIndex] = array1[startScan];
         array2[minIndex] = array2[startScan];
         array1[startScan] = minValue1;
         array2[startScan] = minValue2;
      }
   }

Once you have verified that this is the source of the NullPointerException you have to go back to whereever array1 got its values and see why there is a null at that point. (You should also verify that the value of index is reasonable: ie that you really expect the array to have a nonnull value at that point.)

[pbrockway2]

You populate the salesId array with code like this:

while(inputFile.hasNext())
{
   for (int index  = 0; index < ARRAY_SIZE; index++)
   {
      salesId[index] = inputFile.nextLine();

Can you see that the array may very well end up with nulls in it? If not, print it.

if(fileName.exists())
{
   // etc
}
else
{
   System.out.println("File does not exist");
}
[color=blue]System.out.println("The salesId array:");
for(int i = 0; i < salesId.length;i++)
{
    System.out.print(salesId[i] + " ");
}
System.out.println();[/color]
// etc

[sunde887]

You close the scanner in the array filling loop. You should probably handle the close in a finally