Getting "null" in output with array

Question

Could someone please help me in knowing why my output is off? I know where the error is occuring, but I cant figure out what is going on. Any help is appreciated and I thank you beforehand. Sorry it is so long, but I wanted to provide enough information.
The output for the given input test data is shown below:
Records in original order...
2847 3.89 Arthur C. Clarke
7395 4.00 Rosalind Franklin
4916 3.25 Ryazzudin
9472 2.38 Joe College
4583 0.36 Joe Camel
8365 2.84 Typical J. Student
6395 3.27 Tammy Abel
4962 3.67 R. E. A. C. Paley
Records sorted by ID number...
2847 3.89 Arthur C. Clarke
4583 0.36 Joe Camel
4916 3.25 Ryazzudin
4962 3.67 R. E. A. C. Paley
6395 3.27 Tammy Abel
7395 4.00 Rosalind Franklin
8365 2.84 Typical J. Student
9472 2.38 Joe College
Records sorted by GPA...
7395 4.00 Rosalind Franklin
2847 3.89 Arthur C. Clarke
4962 3.67 R. E. A. C. Paley
6395 3.27 Tammy Abel
4916 3.25 Ryazzudin
8365 2.84 Typical J. Student
9472 2.38 Joe College
4583 0.36 Joe Camel
Records sorted by name...
2847 3.89 Arthur C. Clarke
4583 0.36 Joe Camel
9472 2.38 Joe College
4962 3.67 R. E. A. C. Paley
7395 4.00 Rosalind Franklin
4916 3.25 Ryazzudin
6395 3.27 Tammy Abel
8365 2.84 Typical J. Student
This is the output that I am receiving when I run the below code:
Records in original order...
null
Records sorted by ID Number...
null
Records sorted by GPA...
null
Records sorted by name...
null
<CODE>
import java.io.*;
import java.text.DecimalFormat;
import java.util.StringTokenizer;
public class Pgm06
public static void main(String[] args) throws IOException
final int ARRAY_SIZE = 30;
Student6[] studentArray = new Student6[ARRAY_SIZE];
Student6 student;
int identNum, numStudents;
double gradeAvg;
String fullName;
String sIn;
BufferedReader brIn;
brIn = new BufferedReader(new InputStreamReader(System.in));
DecimalFormat decFmt = new DecimalFormat("0.00");
StringTokenizer tokenizer;
sIn = brIn.readLine();
numStudents = 0;
while(sIn != null)
numStudents++;
tokenizer = new StringTokenizer(sIn);
identNum = Integer.parseInt(tokenizer.nextToken());
gradeAvg = Double.parseDouble(tokenizer.nextToken());
fullName = "";
while(tokenizer.hasMoreTokens())
fullName += tokenizer.nextToken() + " ";
student = new Student6(identNum, gradeAvg, fullName);
studentArray[numStudents - 1] = student;
sIn = brIn.readLine();
} // end while loop
System.out.println("Records in original order...\n" +
studentArray[numStudents]);
Pgm06.selectionSort(studentArray, numStudents, 1);
System.out.println("Records sorted by ID Number...\n" +
studentArray[numStudents]);
Pgm06.selectionSort(studentArray, numStudents, 2);
System.out.println("Records sorted by GPA...\n" +
studentArray[numStudents]);
Pgm06.selectionSort(studentArray, numStudents, 3);
System.out.println("Records sorted by name...\n" +
studentArray[numStudents]);
} // end of main method
public static void selectionSort(Student6[] array, int numStudents,
int criterion)
Student6 temp;
int min;
for (int index = 0; index < numStudents; index++)
min = index;
for (int scan = index + 1; scan < numStudents; scan++)
if(array[min].belongsAfter(array[scan], criterion))
temp = array[scan];
array[scan] = array[min];
array[min] = temp;
} // end of method selectionSort
} // end class Pgm06
>
>
>
<STUDENT CODE>
import java.io.*;
import java.util.StringTokenizer;
public class Student6
private String fullName;
private double gradeAvg;
private int identNum;
public Student6(int IDNumber, double GPA, String name)
identNum = IDNumber;
gradeAvg = GPA;
fullName = name;
} // end constructor Student6
public boolean belongsAfter(Student6 student, int criterion)
if(criterion == 1)
return (identNum > student.identNum);
else if(criterion == 2)
return (gradeAvg < student.gradeAvg);
else if(criterion == 3)
return (fullName.compareTo(student.fullName) > 0);
else
return false;
} // end method belongsAfter
public String toString()
String result;
result = identNum + "\t" + gradeAvg + "\t" + fullName;
return result;
} // end method public String toString
} // end class Student6
<INPUTFILE>
2847 3.89 Arthur C. Clarke
7395 4.00 Rosalind Franklin
4916 3.25 Ryazzudin
9472 2.38 Joe College
4583 0.36 Joe Camel
8365 2.84 Typical J. Student
6395 3.27 Tammy Abel
4962 3.67 R. E. A. C. Paley

Answer 1

Obviously homework, so I'll take a Socratic dialog sort of approach:
What do you think this:
System.out.println("Records in original order...\n" +
                   studentArray[numStudents]);would do, and why?
What is studentArray?
What is numStudents?
What value does numStudents have?
What value does studentArray[numStudents] have? (hint: it's in your output)