Java - 如何在没有别名的情况下返回方法多维数组

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.

Answer 1

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.
}

Answer 2

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.

Answer 3

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 .

Answer 4

You can't return newArr as:

return newArr;

Because it tells the compiler that it is an int but was declared as a 2D array.

Answer 5

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]);
            }
        }
    }
}

Answer 6

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;  
    }      
}

Answer 7

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