Java array :Java pass by reference and pass by value?

Question

I am trying to reverse a Bitmap array, without modifying the source array. But problem is the source array is also getting reversed. Am I doing something wrong or am I suppose to do it some other way? Thanks for help.

private GalleryAdapter galleryAdapter;
private ReverseGalleryAdapter rGalleryAdapter;  

public void onCreate(Bundle savedInstanceState) {
    galleryAdapter = new GalleryAdapter(this, imageThumbnails, imagePaths,
            videoThumbnails, videoPaths);

    imagegrid.setAdapter(galleryAdapter);

    rGalleryAdapter = new ReverseGalleryAdapter(this, reverseBArray(videoThumbnails), reverseSArray(videoPaths),
            reverseBArray(imageThumbnails), reverseSArray(imagePaths));

    imagegrid2.setAdapter(rGalleryAdapter);
}

private Bitmap[] reverseBArray(Bitmap[] v){
    Bitmap[] bTemp;
    bTemp = v;
    int len = bTemp.length;
    Bitmap temp;
    for (int i = 0; i < len/2; i++)
    {
        temp = bTemp[i];
        bTemp[i] = bTemp[len-1 - i];
        bTemp[len-1 - i] = temp;
    }
    return bTemp;
}

private String[] reverseSArray(String[] s){
    String[] sTemp;
    sTemp =s;
    int len = sTemp.length;
    String temp;
    for (int i = 0; i < len/2; i++)
    {
        temp = sTemp[i];
        sTemp[i] = sTemp[len-1 - i];
        sTemp[len-1 - i] = temp;
    }
    return sTemp;
}

Avoid clone as much as possible. Use only when you have no other option. :http://www.javapractices.com/topic/TopicAction.do?Id=71 — Suresh Atta, Oct 07 '13 at 09:00

score 3 · Answer 1 · edited May 23 '17 at 10:25

 Bitmap[] bTemp;
 bTemp = v;

When you are doing this , defenitley both referencing to the same array, because you are not creating a new array there.

same happens here too

  String[] sTemp;
    sTemp =s;

Possible soution :Make copy of array Java (Suggesting to choose after reading possible ways).

My suggestion from Official docs:(See copying array section)

The System class has an arraycopy() method that you can use to efficiently copy data from one array into another:

public static void arraycopy(Object src, int srcPos,
                             Object dest, int destPos, int length)

score 2 · Accepted Answer · answered Oct 07 '13 at 08:38

2

With bTemp = v; you are referring to the same Object.

You can use in your case the clone() method to make a copy of the array:

bTemp = v.clone();

Then you can freely modify it and return it.

answered Oct 07 '13 at 08:38

John

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score 0 · Answer 3 · answered Oct 07 '13 at 08:36

Remember array are object and in method reverseArray, you are reassiging the reference to temp, so now you have 2 references (v , and temp) to same object . Make the appropriate changes mentioned below

private Bitmap[] reverseBArray(Bitmap[] v){
    Bitmap[] bTemp;
    bTemp = v; // CHANGE IT to bTemp = new Bitmap[v.length]
    int len = bTemp.length;
    Bitmap temp;
    for (int i = 0; i < len/2; i++)
    {
        temp = bTemp[i];
        bTemp[i] = bTemp[len-1 - i];
        bTemp[len-1 - i] = temp;
    }
    return bTemp;
}

score 0 · Answer 4 · answered Oct 07 '13 at 08:37

0

I think you want to keep both objects right? If so I think you can use clone() method and pass that cloned object to the method without modifying the original object

answered Oct 07 '13 at 08:37

Thusitha Thilina Dayaratne

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score -1 · Answer 5 · answered Oct 07 '13 at 08:36

-1

Java doesn't have pass objects by value. You pass the array object reference to you method thus the array itself. Best way would be to create a copy of the array and pass the copy of the array.

answered Oct 07 '13 at 08:36

Simon Mokhele

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Java array :Java pass by reference and pass by value?

5 Answers5