How to Randomize Dependent ArrayLists While Maintaining Correspondence?

Automating Randomization of Dependent Lists

When dealing with multiple ArrayLists that are related, it can be useful to be able to randomize them in such a way that they maintain their correspondence. For example, in the case provided, the filelist and imgList ArrayLists have corresponding elements, such as "H1.txt" and "e1.jpg".

Problem Statement

Given two ArrayLists, filelist and imgList, where each element in filelist corresponds to an element in imgList, how can we automatically randomize the order of the elements in imgList to match the randomization of filelist?

Solution

To ensure that the randomization of imgList mirrors the randomization of filelist, we need to use separate Random objects for each list but initialize them with the same seed. This guarantees that both lists will be shuffled in the same manner.

<code class="java">long seed = System.nanoTime();
Collections.shuffle(fileList, new Random(seed));
Collections.shuffle(imgList, new Random(seed));</code>

Explanation

The System.nanoTime() method provides a unique seed value that is based on the current time in nanoseconds. By using this value to initialize both Random objects, we ensure that they generate the same sequence of random numbers. This means that the order of elements in both filelist and imgList will be identical after the shuffling process.

By utilizing this approach, you can achieve the desired random correspondence between the two ArrayLists, where the elements in imgList will follow the same randomized order as the elements in filelist.

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