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    <p><strong>There is no type-safe way to create an array of a parameterized type</strong> such as <code>Iterator&lt;T&gt;[]</code>.</p> <p>Alternatively, you can create a raw array: <code>Iterator&lt;?&gt;[]</code>. Or, if you can avoid the use of arrays entirely, use a collection type like <code>List&lt;Iterator&lt;T&gt;&gt;</code>.</p> <p>The reason it is not possible is that Java arrays are covariant and the parameterized bounds of Generic types are invariant. That is to say:</p> <pre><code>Integer[] integers = new Integer[1]; Number[] numbers = integers; // OK because Integer extends Number numbers[0] = new Double(3.14); // runtime exception </code></pre> <p>The compiler allows the assignment because <code>Double</code> extends <code>Number</code> and the declared type of <code>numbers</code> is <code>Number[]</code>. But at runtime the actual array object instance is the original <code>Integer[1]</code> and arrays know the type of the objects they contain.</p> <p>With generics, parameterized types are different. For one, due to <em>compile-time type erasure</em> they do not intrinsically know their runtime types.</p> <pre><code>List&lt;Integer&gt; integerList = new ArrayList&lt;Integer&gt;(); List&lt;Number&gt; numberList = integerList; // compiler error, prevents: numberList.add(new Double(3.14)); // would insert a Double into integerList Collection&lt;Integer&gt; integerCollection = integerList; // allowed // OK because List extends Collection and the &lt;type parameter&gt; did not change Collection&lt;Number&gt; numberCollection = integerList; // compiler error // an "Integer" is a "Number" // but "a collection of Integers" is more specific than "a collection of Numbers" // and cannot be generally treated the same way and guarantee correct behavior List&lt;?&gt; rawList = integerList; // allowed, but... rawList.add(new Integer(42)); // compiler error, Integer is not a ... a what? </code></pre> <p>With generics, in Java, you are relying on the compiler (not the runtime) to validate that the generic types are correct and safe.</p> <p>So while an <code>Iterator&lt;?&gt;[]</code> knows at runtime that it is an array that contains <code>Iterator</code> elements, the <code>&lt;T&gt;</code> in <code>Iterator&lt;T&gt;[]</code> is <em>erased</em> at compile time and the runtime has no way to know what it was supposed to be. So you get an unchecked warning.</p>
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    1. POHow to safely convert from a Collection of generic types to an array?
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    1. USWilliam Price
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    1. POHow to safely convert from a Collection of generic types to an array?
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    1. CO+1 Good explanation.
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      1. USPaul Bellora
    2. COGood explanation, but, unfortunately, it doesn't help me. I _have_ a Collection<Iterator<T>>, but I _need_ a Iterator<T>[]. I want to convert the former to the latter, and I can do so, but not without a compiler warning. It is only this warning that I want to get rid of.
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      1. USPaul Wagland
    3. CO@PaulWagland: it is impossible to get a non-`null` value of type `Iterator<T>[]` in any way without suppressing a warning somewhere (either in your code or in some function you call)
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