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copied!<p>The behaviour of casting <code>null</code> to an <code>Int</code> depends on the context in which it is done.</p> <p>First of all, if you cast a <code>null</code> to an <code>Int</code>, it actually means a boxed integer, whose value is <code>null</code>. If you put the expression in a context where the expected type is <code>Any</code> (which is translated to <code>Object</code> behind the scene, because in the JVM bytecode, there is no way to refer to a primitive type and a reference type with the same reference), then this value is not converted further - that is why <code>println(null.asInstanceOf[Int])</code> prints <code>null</code>.</p> <p>However, if you use this same boxed integer value in a context where a primitive <code>Int</code> (Java <code>int</code>) is expected, it will be converted to a primitive, and <code>null</code> is (as a default value for reference types) converted to <code>0</code> (a default value for primitive types).</p> <p>If a generic method does this cast, then, naturally, you get a <code>null</code> back.</p> <p>However, if this method is specialized, then its return type is <code>Int</code> (which is a primitive integer in this case), so the <code>null: Any</code> value has to be converted to a primitive, as before.</p> <p>Hence, running:</p> <pre><code>object Test extends App { println(null.asInstanceOf[Int]) def printit(x: Int) = println(x) printit(null.asInstanceOf[Int]) def nullint[T] = null.asInstanceOf[T] println(nullint[Int]) def nullspecint[@specialized(Int) T] = null.asInstanceOf[T] println(nullspecint[Int]) } </code></pre> <p>produces:</p> <pre><code>null 0 null 0 </code></pre>

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