Array Index out of Bound exception in a program for reverse of an array

Question

Here is the code to reverse an array

import java.util.*;
class middle {
    public static void main(String args[]){
        int a[]=new int[]{2,3,65,4,7,8,9};
        int c[]=new int[a.length-1];
        int k=0;
        for(int i=a.length;i>0;i++){
            c[k]=a[i];
            k++;
        }

        System.out.println("Reverse of an array");
        for(int i=0;i<c.length;i++)
            System.out.print(c[i]+"   ");
    }
}

while running gives Array index out of bound exception:7 where the code is going wrong?

array[array.length] will always be out of bounds. Array indices go from 0 to length-1. See also the official tutorial on arrays. — Jason C
– Jason C, Commented Apr 12, 2014 at 16:38
Please please PLEASE format your code. Also, please use Java naming conventions - classes should be in PascalCase; Middle not middle. — Boris the Spider
– Boris the Spider, Commented Apr 12, 2014 at 16:38

Jigar Joshi · Accepted Answer · 2014-04-12 16:36:34Z

1

a.length is out of bound for a

for(int i=a.length;i>0;i++)
{
 c[k]=a[i];
 k++;
}

then,

int c[]=new int[a.length-1];

you need same length array for, not length - 1 for reverse array

answered Apr 12, 2014 at 16:36

Jigar Joshi

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1 Comment

Jigar Joshi Over a year ago

@Raju your comment doesn't support -1

Azar · Accepted Answer · 2014-04-12 16:53:54Z

1

To loop through the array backwards, you need to change all three conditions in your loop, like so:

for(int i=a.length-1;i>=0;i--)
{
 c[k]=a[i];
 k++;
}

Let's take this apart:

int i=a.length-1;

You must begin at a.length-1, as arrays use 0-based indexing and a.length is out of bounds.

i>=0;

You need to iterate until i>=0, as i>0 will miss one element of your array.

i--

You need to decrement i, as the loop will always access out of bounds indexes/never terminate otherwise.

P.S. As @Jigar mentioned, you need to initialize c as int c[]=new int[a.length];.

edited Apr 12, 2014 at 16:53

answered Apr 12, 2014 at 16:38

Azar

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Comments

Raju Sharma · Accepted Answer · 2014-04-12 16:49:07Z

0

you did mistake here , you need to mention the length of array a.length not a.length-1 for c and the values in for loop conditions should have like for(int i=a.length-1;i>=0;i--) i should be decremented. : modified code is here:

int a[]=new int[]{2,3,65,4,7,8,9};
int c[]=new int[a.length];

int k=0;
for(int i=a.length-1;i>=0;i--)
{

c[k]=a[i];
k++;

}

edited Apr 12, 2014 at 16:49

answered Apr 12, 2014 at 16:40

Raju Sharma

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1 Comment

Jason C Over a year ago

This answer would be more useful if you pointed out the mistakes and explained why your modifications solve the issues. :)

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