Create a reverse order array from given array

Question

I have an assignment to create a class in which I create an array of size 10, called source, and assign random integers in the range 0-10 to all indexes in it, and then call a method that creates a new array in reverse order. I tried the code below:

public class Exercise7_4 {

    // reverse array method
    public static int[] reverseArray(int[] arr) {
        int[] reverse = new int[arr.length];

        for (int i = 0; i < reverse.length - 1; i++) {
            reverse[i] = arr[arr.length - 1 - i];
        }

        return reverse;
    }

    // print array in ascending order
    public static void printArray(int[] arr) {

        for (int i = 0; i < arr.length - 1; i++) {
            System.out.printf("%d\t", arr[i]);
        }

        System.out.println();
    }

    public static void main(String[] args) {
        int[] source = new int[10];

        for (int i = 0; i < source.length - 1; i++) {
            source[i] = (int) (Math.random() * 10 + 1);
        }

        int[] reverse = reverseArray(source);
        printArray(source);
        printArray(reverse);
    }
}

The problem is that the output i get looks like this:

7   1   3   7   10  9   6   2   6   
0   6   2   6   9   10  7   3   1

meaning, the reverseArray method doesn't work properly on reverse[0] for some reason.

I would like to know why this is happening and how I can fix it. Thanks in Advance!

in your for loops you iterate from 0 to arr.length - 2 and reverse.length - 2. Change your loops to resemble for (int i = 0; i < reverse.length; i++) instead of for (int i = 0; i < reverse.length - 1; i++) — Jonny Henly
– Jonny Henly, Commented Dec 15, 2015 at 9:06

ParkerHalo · Accepted Answer · 2015-12-15 09:13:14Z

2

change all your for-loops from

for (int i = 0; i < source.length - 1; i++)

to

for (int i = 0; i < source.length; i++)

Your reverse method is completely correct (if you change the loop). The mistake you made is that you created an array of size 10, filled it with 9 random values (the value of index 10 will therefore be 0).

answered Dec 15, 2015 at 9:13

ParkerHalo

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Comments

Jose Luis · Accepted Answer · 2015-12-15 09:22:37Z

You could check wich index are consulted in each iteration of your for loop.

This is your solution

    for (int i = 0; i < reverse.length - 1; i++) {
        System.out.println("" + i + " " +  (reverse.length - 1 - i));        
    }

And it prints:

The 'i' don't get the value 9, and the (reverse.length - 1 - i) don't get the value 0.

Changing the testing condition for this:

i < reverse.length

gives you the last position:

9  0

Kruti Patel · Accepted Answer · 2015-12-15 09:15:50Z

1

Change reverseArray function as follows:

public static int[] reverseArray(int[] arr) {

int[] reverse = new int[arr.length];

for (int i = 0; i < reverse.length; i++) {

    reverse[i] = arr[arr.length - i];

}


return reverse;

}

You need not to -1 from arr.length.

Change another for loop also:

for (int i = 0; i < source.length; i++) {

    source[i] = (int) (Math.random() * 10 + 1);

}

Here, also you do not need to do -1 from source.length.

edited Dec 15, 2015 at 9:15

answered Dec 15, 2015 at 9:09

Kruti Patel

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3 Comments

Kruti Patel Over a year ago

@JonnyHenly: Ya. But he has create array of 9 elements only. That's why.

Kruti Patel Over a year ago

i < source.length - 1 which means i<(11-1) which will turn into 9 elements.

Nitzan M Over a year ago

Thanks @KrutiPatel that's worked. It was really a newbie mistake.

Anil M · Accepted Answer · 2016-10-16 17:20:05Z

0

package com.test;

public class SortArray {

private int[] getSortedArry(int[] arr){

    int arrLen = arr.length;
    int reversedArry[] = new int[arrLen]; 
    System.out.println("array lenght: " +arr.length);
    int j = 0;
    for(int i=arrLen-1; i>=0; i--){

        reversedArry[j] = arr[i];


        j++;

    }
    System.out.print("\n");
    return reversedArry;

}

public static void main(String[] args){

    int arr[] = {10,2,3,4,5,12,23,43,45,65};

    SortArray sortArray = new SortArray();
    int reversedArry[] = sortArray.getSortedArry(arr);

    for(int i=0;i<reversedArry.length;i++){
        System.out.print(reversedArry[i] + " ");    

    }


}

}

answered Oct 16, 2016 at 17:20

Anil M

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