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    <p><strong>The code generate a random <a href="http://en.wikipedia.org/wiki/Permutation" rel="nofollow noreferrer">permutation</a> of the original array.</strong></p> <p>However, note that this is biased - it does not generate all permutations in uniform distribution. <a href="https://stackoverflow.com/questions/5131341/what-distribution-do-you-get-from-this-broken-random-shuffle">This thread</a> discusses what is the affect of this bias.</p> <p>To overcome this issue - you might want to have a look on <strong><a href="http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle" rel="nofollow noreferrer">fisher yates shuffle</a></strong> (which main difference is, to generate a random number in range [i,n) in each iteration instead of in range [0,n).)</p> <hr> <p><strong>EDIT:</strong> <br>You might better understand it if you encapsulate the assignments in a method:</p> <pre><code>private static void swap(int[] array, int i, int j) { tempNum = array[j]; array[j] = array[i]; array[i]=tempNum; } </code></pre> <p>Now, the code will be simpler to follow:</p> <pre><code>for(int i = 0; i&lt; leftbut.length; i++) { //choose a random index in the array int randomNumber =(int)(Math.random()*leftbut.length); //swap the element in index i with the random element chosen in the array swap(leftbut, i, randomNumber); } </code></pre> <p>The idea is you <code>swap()</code> each element in the array with a random index. This random index is chosen randomly from the array, and its index is denoted as <code>randomNumber</code>. <br>Since you only <code>swap()</code> items around, you can easily prove that the output array is a permutation of the original.</p>
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    1. COAll the 9 buttons contain an ImageIcon. If this code randomly generates numbers which shuffles the JButton. There will be duplicate buttons with duplicate ImageIcon no?
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    2. CO@user2016977 A permutation contains no doubles, so if the elements in the original list are all unique, the result list will have all elements unique as well.
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    3. COWhat is a simple way to explain this?
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