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

Use Collections.shuffle() twice, with two Random objects initialized with the same seed:

long seed = System.nanoTime();
Collections.shuffle(fileList, new Random(seed));
Collections.shuffle(imgList, new Random(seed));

Using two Random objects with the same seed ensures that both lists will be shuffled in exactly the same way. This allows for two separate collections.