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    <pre><code>java.util.Collections.shuffle(java.util.Arrays.asList(a:_*)) </code></pre> <p>For the above to work correctly, a's element type has to be a subclass of scala.AnyRef (equivalent to java.lang.Object) because Arrays.asList() uses the array passed in as the backing store for the result java.util.List and java.util.List can contain only object references (not primitive values).*</p> <p>That is also the reason why Collections.shuffle() which shuffles the passed-in java.util.List actually shuffled the array.*</p> <p>*: See the note below</p> <p>For example:</p> <pre><code>scala&gt; val a = Array[java.lang.Integer](1, 2, 3) // note the type parameter a: Array[java.lang.Integer] = Array(1, 2, 3) scala&gt; java.util.Collections.shuffle(java.util.Arrays.asList(a:_*)) scala&gt; a res43: Array[java.lang.Integer] = Array(1, 3, 2) scala&gt; java.util.Collections.shuffle(java.util.Arrays.asList(a:_*)) scala&gt; a res45: Array[java.lang.Integer] = Array(1, 2, 3) </code></pre> <p>Note: Scala 2.7.5 is used for the above code snippets. Scala 2.8.0 exhibits different behaviors as Daniel demonstrated. To be on the safe side, do not depend on the fact that the array gets shuffled but instead the list that is returned from Arrays.asList() gets shuffled.</p> <pre><code>scala&gt; val a = Array[java.lang.Integer](1, 2, 3) a: Array[java.lang.Integer] = Array(1, 2, 3) scala&gt; val b = java.util.Arrays.asList(a:_*) b: java.util.List[java.lang.Integer] = [1, 2, 3] scala&gt; java.util.Collections.shuffle(b) scala&gt; b res50: java.util.List[java.lang.Integer] = [2, 1, 3] scala&gt; java.util.Collections.shuffle(b) scala&gt; b res52: java.util.List[java.lang.Integer] = [3, 1, 2] </code></pre>
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    1. POHow to use Java Collections.shuffle() on a Scala array?
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    1. COThanks. But that doesn't work for a Scala array with integers - it results in a ClassCastException, because the array can't be cast to a Java array of Objects.
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    2. CO@Jesper For the Collections.shuffle() to work, make sure the array contains object references and not primitive values. (scala.Int -> java.lang.Integer, scala.Long -> java.lang.Long, etc) I've edited the answer to emphasize this point.
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