Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException error in java

Question

I'm now writing a quicksort program in java and encountered an error. The terminal says that

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 101 out of bounds for length 19
    at QuickSort.swap(qs.java:16)
    at QuickSort.partition(qs.java:23)
    at QuickSort.quickSort(qs.java:9)
    at QuickSort.quickSort(qs.java:5)
    at QuickSort.main(qs.java:40)

this is my first programming in java and this error did not occur when I tested this with an array that is a size of 10 and another array that has the same size to the array in the following program.

I did my research and this error occurs when the program access the wrong indexed array or out of range of loops but it works with other arrays that have the same size.

import java.util.Arrays;

public class QuickSort {
    public void quickSort(int[] A) {
    quickSort(A, 0, A.length - 1);
    }
    private void quickSort(int[] A, int low, int high) {
        if (low < high + 1) {
            int p = partition(A, low, high);
            quickSort(A, low, p - 1);
            quickSort(A, p + 1, high);
        }
    }

    private void swap(int[] A, int index1, int index2) {
        int temp = A[index1];
        A[index1] = A[index2];
        A[index2] = temp;
    }

    private int getPivot(int[] A, int low, int high) {
        return A[low];
    }

    private int partition(int[] A, int low, int high) {
        swap(A, low, getPivot(A, low, high));
        int border = low + 1;
        for (int i = border; i <= high; i++) {
            if (A[i] < A[low]) {
                swap(A, i, border++);
            }
        }
        swap(A, low, border - 1);
        return border - 1;
    }

    public static void main(String[] args) {
        QuickSort qs = new QuickSort();
        int[] A = {101,103,102,107,110,116,114,118,112,111,109,104,117,100,105,115,113,106,119};
        System.out.println(Arrays.toString(A));

        long start = System.nanoTime();

        qs.quickSort(A);

        long end = System.nanoTime();

        long elapsed_secs = end - start;
        double seoconds = (double)elapsed_secs / 1_000_000_000.0;

        System.out.println(Arrays.toString(A));
        System.out.println(seoconds);
    }
}

VietDD · Answer 1 · 2018-11-27T02:44:09.950

0

Check this

private int getPivot(int[] A, int low, int high) {
    return A[low];
}

With

int[] A = {101,103,102,107,110,116,114,118,112,111,109,104,117,100,105,115,113,106,119};

At first time, low is 101 -> get value A at index 101, but size of A is 19 -> Exception

What do you want to do with getPivot ?

Just by comment

swap(A, low, getPivot(A, low, high));

Result :

[101, 103, 102, 107, 110, 116, 114, 118, 112, 111, 109, 104, 117, 100, 105, 115, 113, 106, 119]
[100, 101, 102, 103, 104, 105, 106, 107, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119]

edited Nov 27 '18 at 02:44

answered Nov 27 '18 at 02:35

VietDD

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the getPivot was originally a function that returns a pivot that pointing the middle value of the vectors, but I wanted to make it point the first value of each vector how should I edit it to prevent this error? – A.Lee Nov 27 '18 at 04:29
so just return low instead of return A[low] ? – VietDD Nov 27 '18 at 04:49

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException error in java

1 Answers1