System.arraycopy returning arrayoutofboundsexception

Question

I learnt about the arraycopy() function in java today and I was working with it in a code . But I was constantly getting an ArrayOutOfBoundsException. I tried to figure out a solution and searched on google for solutions but I can't seem to solve it. It would be helpful , if someone can take a look at it

System.arraycopy(a, 0, b, 1, N + 1);

Here, "a" is an array of length "N", and b is another array of length"N+1" I want to copy all the elements of array "a" to array "b" in such a way that , all the elements of array "a" are start from the 2nd index of array "b", leaving space for another element in array "b"

Here is the whole code if any requires it:

import java.util.Random;
import java.util.Scanner;

public class JavaApplication24 {

public static long DC;
public static long DM1;
public static long DM;

private static int[] Insrtn_sort(int[] a, int N) {

    int t, i;
    int b[] = new int[N + 1];
    DC = 0;
    DM = 0;
    DM1 = 0;

    b[0] = Integer.MIN_VALUE;
    System.arraycopy(a, 0, b, 1, N + 1);

    for (int j = 1; j < N + 1; j++) {
        t = b[j];
        i = j - 1;
        while (t < b[i]) {
            b[i + 1] = b[i];
            i--;
            DC++;
            DM1++;
        }
        b[j + 1] = t;
        DM++;
    }

    return b;
}

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    Random r = new Random();
    float StartTime, EndTime, TotalTime;

    int N = sc.nextInt();
    int[] a = new int[N];
    for (int i = 0; i <= N - 1; i++) {
        a[i] = r.nextInt();
    }

    StartTime = System.currentTimeMillis() / 1000;
    Insrtn_sort(a, N);
    EndTime = System.currentTimeMillis() / 1000;

    TotalTime = StartTime - EndTime;

    for (int i = 1; i <= N - 1; i++) {
        System.out.println(a[i]);
    }
    System.out.println("Time taken for sorting: " + TotalTime);
    System.out.println("Total number of data comparisons: " + DC);
    System.out.println("Total number of data movements: " + DM + DM1);

}

}

FYI, i <= N - 1 is equivalent to the shorter and more conventional i < N. — shmosel
– shmosel, Commented May 17, 2017 at 4:03

Yashar Aliabbasi · Accepted Answer · 2017-05-17 03:36:23Z

3

Your a array Index is from 0 to [N-1] with length of(N) and b array index is from 0 to N with length of (N+1) then you must write System.arraycopy(a, 0, b, 1, N );

answered May 17, 2017 at 3:36

Yashar Aliabbasi

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GhostCat · Accepted Answer · 2017-05-17 03:42:08Z

3

See the @param length in the source of System.arraycopy:

@param length the number of array elements to be copied.

so the N+1 must be N means the number you want to copy, just as the length of array "a"

edited May 17, 2017 at 3:42

GhostCat

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answered May 17, 2017 at 3:38

zhenxianyimeng

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