Thread: Error message java.lang.ArrayIndexOutOfBoundsException: 0

Hey guys, this is my first time on here so I don't know if my code is going to come out messy, so if it does I'm sorry. I'm new to java programming and I'm working on an assignment where I was given the main method and one constructor class, and I had to create the other constructor class myself. However when I run the program, the main method complains at the line:

int size = Integer.parseInt(args[0]);

And says "java.lang.ArrayOutOfBoundsException: 0" I'm not sure what this means, but here is my constructor class StudentCollection along with the main method if that helps. Could anyone tell me what I am doing wrong?

public class StudentCollection
{
    private double averageGPA;
    private int count;
    private Student[] collection;
 
    public StudentCollection(int initialSize){
        collection=new Student[initialSize];
        count=0;
    }
 
    public void addToCollection(Student s) {
        if(count==collection.length) {
            increaseSize();
        }
        collection[count]=s;
        count++;
    }
 
    private void increaseSize() {
        Student[] collection2=new Student[collection.length*2+1];
        System.arraycopy(collection, 0, collection2, 0, count);
        collection=collection2;
    }
 
    public double getAverageCreditsCompleted() {
        double sum=0;
        if(count>0) {
            for(int i=0; i<count; i++) {
                sum=sum+collection[i].getCreditsCompleted();
            }
            return sum/count;
        }
            else return 0;
    }
 
    public double getAverageGPA() {
        double sum=0;
        if(count>0) {
        for(int i=0; i<count; i++) {
            sum=sum+collection[i].getGPA();
        }
        return sum/count;
      }
        else return 0;
    }
 
    public int getCount() {
        return count;
    }
 
    public boolean removeFromCollection(java.lang.String name) {
        for(int i=0; i<count; i++) {
            if(collection[i].getName().toUpperCase().equals(name.toUpperCase())) {
            collection[i]=collection[count-1];
            count--;
            return true;
        }
           else return false;
       }
       return false;
    }
 
    public String toString() {
        String stuString="";
            for(int i=0; i<count; i++) {
                stuString=stuString+collection[i];
            }
            return stuString;
    }
 }

And here is the main method:

public class Lab8  {
    public static void main (String[] args)  {
        // Scanner to read input from the keyboard
        Scanner keyboard = new Scanner(System.in);
        int size = Integer.parseInt(args[0]);  // use "2" when you run the program
 
        StudentCollection collection = new StudentCollection(size);
        Student s;  // s is a Null reference at this point
        String name, major;
        int credits;
        double gpa;
        int choice;
        DecimalFormat df = new DecimalFormat("0.00");
 
        String line;
 
        do {
            System.out.println();
            System.out.println("\t1. Add a new Student to the collection");
            System.out.println("\t2. Remove a Student from the collection");
            System.out.println("\t3. Display the students in the collection");
            System.out.println("\t4. Display statistics");
            System.out.println("\t5. Quit the program");
 
            System.out.print("\nYour selection: ");
            choice = Integer.parseInt(keyboard.nextLine() );
 
            switch(choice) {
               case 1: 
                   System.out.print("Enter the student's full name: ");
                   name = keyboard.nextLine();
 
                   System.out.print("Enter the students gpa: ");
                   line = keyboard.nextLine();
                   gpa = Double.parseDouble(line);
 
                   System.out.print("Enter the student's major: ");
                   major = keyboard.nextLine();
 
                   System.out.print("Enter the number of credits completed by the student: ");
                   line = keyboard.nextLine();
                   credits = Integer.parseInt(line);
 
                   s = new Student(name, gpa, major, credits);
                   collection.addToCollection(s);
                   break;
 
               case 2:
                   System.out.print("Enter the name of the student that is to be removed: ");
                   name = keyboard.nextLine();
                   boolean result = collection.removeFromCollection(name);
                   if (result) 
                      System.out.println("Student with name " + name  + " is successfully removed");
                   else
                       System.out.println("There is no Student whose name is " + name);
                   break;
 
               case 3:
                   System.out.println(collection);
                   break;
 
               case 4:
                   System.out.println("There are " + collection.getCount() + " students in the collection");
                   System.out.println("Average GPA of the students in the collection: " +
                               df.format(collection.getAverageGPA() ));
                   System.out.println("Average number of credits completed by the students " +
                               "in the collection: " + collection.getAverageCreditsCompleted() );
                   System.out.println();
                   break;
 
               case 5:
                   System.out.println("Thank you for using my program.  Good bye!");
                   System.exit(0);   // quit the program
 
               default:
                   System.out.println("Illegal Choice.  Try again");
            }   // end of switch
        } while (choice != 5);   
    }  // main method
}

Thank you, I appreciate the help.

Originally Posted by Norm

Use the array field: .length to test the length: if(theArray.length > 0) ...

How will this stop the error message from happening? And where do I put this if statement?

Isn't it supposed to be empty at index 0? That's where I'm supposed to put my first student object. If I don't index into it, won't that just stop the execution of the program since the if statement won't be met? I'm sorry, I'm really new to this, I have trouble understanding most things with arrays.

That is all the compiler tells me for the error sir, and it highlights the line

int size = Integer.parseInt(args[0]);