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/**
* Phantom reference objects, which are enqueued after the collector
* determines that their referents may otherwise be reclaimed. Phantom
* references are most often used to schedule post-mortem cleanup actions.
+ * <p>
+ * The referent must not be an instance of a {@linkplain Class#isValue()
+ * value class}; such a value can never have another reference to it
+ * and cannot be held in a reference type.
*
* <p> Suppose the garbage collector determines at a certain point in time
* that an object is <a href="package-summary.html#reachability">
* phantom reachable</a>. At that time it will atomically clear
* all phantom references to that object and all phantom references to
* queue. Such a reference will never be enqueued.
*
* @param referent the object the new phantom reference will refer to
* @param q the queue with which the reference is to be registered,
* or {@code null} if registration is not required
+ * @throws IllegalArgumentException if the referent is an instance of an
+ * {@link Class#isValue() value class}
*/
public PhantomReference(T referent, ReferenceQueue<? super T> q) {
super(referent, q);
}
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