Array out of bounds on a recursive insertion sort on an array

Question

New to the forums, just have a quick question. I am trying to figure out how to write the insertion sort algorithm recursively. Recursion is still quite confusing to me.

When I run my program I receive an Array out of bounds exception and am wondering what exactly is causing this and why.

I am inserting 25 ints: 25 67 13 98 30 22 47 52 11 20 76 13 9 53 86 21 7 45 68 29 18 93 44 50 62.

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Scanner;


class ArrayIns {
private int[] a;
private int nElems;

public ArrayIns(int max) {
    a = new int[max];
    nElems = 0;
}

public void insert(int value) {
    a[nElems] = value;
    nElems++;
}

public void display() {
    for (int j = 0; j < nElems; j++) {
        System.out.print(a[j] + " "); 
    }
    System.out.println("");
}

public void insertionSort() {
    insertSortRecursive(nElems - 1);
}

private void insertSortRecursive(int index) {
    int i;
    if (index < 1) {
    } else {
        insertSortRecursive(index - 1);

        int key = a[index];
        i = index - 1;

        while(index >= 0 && a[i] > key) {
            a[i+1] = a[i];
            i = i - 1;
        } // while
    } // else
} // End of recursiveSort
} // ArrayIns

class InsertSortApp {
public static void main(String[] args) throws FileNotFoundException {
    int maxSize = 50;
    ArrayIns arr;
    arr = new ArrayIns(maxSize);

    Scanner inputFile;

    inputFile = new Scanner (new FileReader("int.dat"));

    while(inputFile.hasNext()) {
        int in = inputFile.nextInt();
        arr.insert(in);
    }

    arr.display();

    inputFile.close();
}
} // End of insertsortapp

Answer 1

You are not calling the sort function yet, so the problem isn't with you recursion algorithm. I think it is with your file reader while loop, it is adding more than 50 "integers".

The best would be print out a counter to see how many loops it goes through (omit the insert to test your while loop).

Try:

inputFile = new Scanner (new FileReader("int.dat"));

while(inputFile.hasNextInt()) {
    int in = inputFile.nextInt();
    arr.insert(in);
}