How to randomize two ArrayLists in the same fashio

Question

I have two arraylist filelist and imgList which related to each other, e.g. "H1.txt" related to "e1.jpg". How to automatically randomized the list of imgList according to the randomization of fileList? Like in excel, if we sort certain column, the other column will automatically follow?

String [] file = {"H1.txt","H2.txt","H3.txt","M4.txt","M5.txt","M6.txt"};
ArrayList<String> fileList = new ArrayList<String>(Arrays.asList(file));

String [] img = {"e1.jpg","e2.jpg","e3.jpg","e4.jpg","e5.jpg","e6.jpg"};
ArrayList<String> imgList = new ArrayList<String>(Arrays.asList(img));

//randomized files
Collections.shuffle(fileList);

output after randomization e.g.:

fileList = {"M4.txt","M6.txt","H3.txt","M5.txt","H2.txt","H1.txt"};

intended output:

 imgList = {"e4.jpg","e6.jpg","e3.jpg","e5.jpg","e2.jpg","e1.jpg"};

Answer 1

This can be done using the shuffle method:

private List<Integer> getJumbledList() {
     List<Integer> myArrayList2 = new ArrayList<Integer>();
        myArrayList2.add(8);
        myArrayList2.add(4);
        myArrayList2.add(9);
        Collections.shuffle(myArrayList2);
        return myArrayList2;

Answer 2

Unless there's a way to retrieve the old index of the elements after they've been shuffled, I'd do it one of two ways:

A) Make another list multi_shuffler = [0, 1, 2, ... , file.size()] and shuffle it. Loop over it to get the order for your shuffled file/image lists.

ArrayList newFileList = new ArrayList(); ArrayList newImgList = new ArrayList(); for ( i=0; i

or B) Make a StringWrapper class to hold the file/image names and combine the two lists you've already got into one: ArrayList combinedList;

Answer 3

Wrap them in another class so that you can end up with a single array or List of those objects.

public class Data {
    private String txtFileName;
    private String imgFileName;

    // Add/generate c'tor, getter/setter, equals, hashCode and other boilerplate.
}

Usage example:

List<Data> list = new ArrayList<Data>();
list.add(new Data("H1.txt", "e1.jpg"));
list.add(new Data("H2.txt", "e2.jpg"));
// ...

Collections.shuffle(list);