Java - how to return in a method multidimensional array without aliasing

Question

I'm aware that arrays are objects and in java objects are transfered by reference which could cause aliasing so objects should be returned with in this form to not cause aliasing:

return new (object(parameters));

So this is what I'm trying to do with multidimensional arrays, however for some reason compiler says I have an error : "array dimension missing".

public int[][] Testing(int[][]arr)
    {
        int[][]newArr=new int[arr.length][arr[0].length];
        for(int i=0;i<arr.length;i++)
        {
            for(int j=0;j<arr[0].length;j++)
            {
                newArr[i][j]=arr[i][arr[0].length-1-j];
            }
            return new int[][]newArr;  
        }      
    }

Could anyone tell me how to return in a method an multidimensional array without aliasing?

Thank you.

Ruchira Gayan Ranaweera · Accepted Answer · 2013-12-11 12:26:54Z

4

return newArr; is the one you should use. Change your code as follows

  public int[][] Testing(int[][]arr){
    int[][]newArr=new int[arr.length][arr[0].length];
    for(int i=0;i<arr.length;i++)
    {
        for(int j=0;j<arr[0].length;j++)
        {
            newArr[i][j]=arr[i][arr[0].length-1-j];
        }

    }
    return newArr; // rerunning the array witch created inside this method.
}

answered Dec 11, 2013 at 12:26

Ruchira Gayan Ranaweera

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Comments

Keppil · Accepted Answer · 2013-12-11 12:29:05Z

1

Since you are creating your array inside your method, there is no risk for aliasing in this scenario. Noone else can get a reference to your array.

A simple

return newArr;

will work just fine.

answered Dec 11, 2013 at 12:29

Keppil

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Comments

Community · Accepted Answer · 2017-05-23 12:32:11Z

0

Do you want to return a copy of newArr? see the following: copy a 2d array in java

If you don't need a copy - just return newArr.

edited May 23, 2017 at 12:32

CommunityBot

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answered Dec 11, 2013 at 12:31

Lital Kolog

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Comments

Syed mohamed aladeen · Accepted Answer · 2019-05-17 12:18:24Z

0

import java.util.Scanner;
public class First {
    int a[][]=new int[3][3];
    Scanner s=new Scanner(System.in);
    int[][] Arr()
    {
        for(int i = 0;i < a.length;i++)
        {
            for(int j = 0;j < a.length;j++)
            {
                a[i][j] = s.nextInt();
            }
        }
        return(a);
    }
    public static void main(String[] args) {
        First f = new First();
        int c[][]=new int[3][3];
        c=f.Arr();
        for(int i=0;i<c.length;i++)
        {
            for(int j=0;j<c.length;j++)
            {
                System.out.println(c[i][j]);
            }
        }
    }
}

edited May 17, 2019 at 12:18

Syed mohamed aladeen

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answered May 17, 2019 at 11:57

Ajay kumar

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Comments

Suraj Adhikary · Accepted Answer · 2019-09-02 04:19:19Z

0

you should return newArr instead of int[][]newArr.

public int[][] Testing(int[][]arr)
{
    int[][]newArr=new int[arr.length][arr[0].length];
    for(int i=0;i<arr.length;i++)
    {
        for(int j=0;j<arr[0].length;j++)
        {
            newArr[i][j]=arr[i][arr[0].length-1-j];
        }
        return new newArr;  
    }      
}

answered Sep 2, 2019 at 4:19

Suraj Adhikary

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Comments

AMIT SINGH BISHT · Accepted Answer · 2020-12-25 05:18:37Z

0

public int[][] Testing(int[][] arr){
    int[][] newArr = new int[arr.length][arr[0].length];
    for(int i = 0; i < arr.length; i++){
        for(int j = 0; j < arr[0].length; j++){       
            newArr[i][j] = arr[i][arr[0].length-1-j];
        }            
    }    
    return newArr; 
}

Note: If you directly print the newArr in your main method you will get an error [[Ljava.lang.String;@

To avoid this use for loop to print your array output

edited Dec 25, 2020 at 5:18

answered Dec 25, 2020 at 5:02

AMIT SINGH BISHT

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