Check out example codes for "generate random number in java within a range without repeating with android studio". It will help you in understanding the concepts better.

Code Example 1

public void NextRandom(View view) // button clicked function
    {
        int previousIndex = index;
        index = rand.nextInt(array.size());

        while (index == previousIndex)
        {
            index = rand.nextInt(array.size());
        }
    }

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