63  *   This set is returned by the {@link #selectedKeys() selectedKeys} method.
  64  *   The selected-key set is always a subset of the key set. </p></li>
  65  *
  66  *   <li><p> The <i>cancelled-key</i> set is the set of keys that have been
  67  *   cancelled but whose channels have not yet been deregistered.  This set is
  68  *   not directly accessible.  The cancelled-key set is always a subset of the
  69  *   key set. </p></li>
  70  *
  71  * </ul>
  72  *
  73  * <p> All three sets are empty in a newly-created selector.
  74  *
  75  * <p> A key is added to a selector's key set as a side effect of registering a
  76  * channel via the channel's {@link SelectableChannel#register(Selector,int)
  77  * register} method.  Cancelled keys are removed from the key set during
  78  * selection operations.  The key set itself is not directly modifiable.
  79  *
  80  * <p> A key is added to its selector's cancelled-key set when it is cancelled,
  81  * whether by closing its channel or by invoking its {@link SelectionKey#cancel
  82  * cancel} method.  Cancelling a key will cause its channel to be deregistered
  83  * during the next selection operation, at which time the key will removed from
  84  * all of the selector's key sets.
  85  *
  86  * <a id="sks"></a><p> Keys are added to the selected-key set by selection
  87  * operations.  A key may be removed directly from the selected-key set by
  88  * invoking the set's {@link java.util.Set#remove(java.lang.Object) remove}
  89  * method or by invoking the {@link java.util.Iterator#remove() remove} method
  90  * of an {@link java.util.Iterator iterator} obtained from the set.
  91  * All keys may be removed from the selected-key set by invoking the set's
  92  * {@link java.util.Set#clear() clear} method.  Keys may not be added directly
  93  * to the selected-key set. </p>
  94  *
  95  * <a id="selop"></a>
  96  * <h2>Selection</h2>
  97  *
  98  * <p> A selection operation queries the underlying operating system for an
  99  * update as to the readiness of each registered channel to perform any of the
 100  * operations identified by its key's interest set.  There are two forms of
 101  * selection operation:
 102  *
 103  * <ol>
 104  *

  63  *   This set is returned by the {@link #selectedKeys() selectedKeys} method.
  64  *   The selected-key set is always a subset of the key set. </p></li>
  65  *
  66  *   <li><p> The <i>cancelled-key</i> set is the set of keys that have been
  67  *   cancelled but whose channels have not yet been deregistered.  This set is
  68  *   not directly accessible.  The cancelled-key set is always a subset of the
  69  *   key set. </p></li>
  70  *
  71  * </ul>
  72  *
  73  * <p> All three sets are empty in a newly-created selector.
  74  *
  75  * <p> A key is added to a selector's key set as a side effect of registering a
  76  * channel via the channel's {@link SelectableChannel#register(Selector,int)
  77  * register} method.  Cancelled keys are removed from the key set during
  78  * selection operations.  The key set itself is not directly modifiable.
  79  *
  80  * <p> A key is added to its selector's cancelled-key set when it is cancelled,
  81  * whether by closing its channel or by invoking its {@link SelectionKey#cancel
  82  * cancel} method.  Cancelling a key will cause its channel to be deregistered
  83  * during the next selection operation, at which time the key will be removed
  84  * from all of the selector's key sets.
  85  *
  86  * <a id="sks"></a><p> Keys are added to the selected-key set by selection
  87  * operations.  A key may be removed directly from the selected-key set by
  88  * invoking the set's {@link java.util.Set#remove(java.lang.Object) remove}
  89  * method or by invoking the {@link java.util.Iterator#remove() remove} method
  90  * of an {@link java.util.Iterator iterator} obtained from the set.
  91  * All keys may be removed from the selected-key set by invoking the set's
  92  * {@link java.util.Set#clear() clear} method.  Keys may not be added directly
  93  * to the selected-key set. </p>
  94  *
  95  * <a id="selop"></a>
  96  * <h2>Selection</h2>
  97  *
  98  * <p> A selection operation queries the underlying operating system for an
  99  * update as to the readiness of each registered channel to perform any of the
 100  * operations identified by its key's interest set.  There are two forms of
 101  * selection operation:
 102  *
 103  * <ol>
 104  *