1 /*
   2  * Copyright (c) 2007, 2009, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.nio.file;
  27 
  28 /**
  29  * An event or a repeated event for an object that is registered with a {@link
  30  * WatchService}.
  31  *
  32  * <p> An event is classified by its {@link #kind() kind} and has a {@link
  33  * #count() count} to indicate the number of times that the event has been
  34  * observed. This allows for efficient representation of repeated events. The
  35  * {@link #context() context} method returns any context associated with
  36  * the event. In the case of a repeated event then the context is the same for
  37  * all events.
  38  *
  39  * <p> Watch events are immutable and safe for use by multiple concurrent
  40  * threads.
  41  *
  42  * @param   <T>     The type of the context object associated with the event
  43  *
  44  * @since 1.7
  45  */
  46 
  47 public interface WatchEvent<T> {
  48 
  49     /**
  50      * An event kind, for the purposes of identification.
  51      *
  52      * @since 1.7
  53      * @see StandardWatchEventKind
  54      */
  55     public static interface Kind<T> {
  56         /**
  57          * Returns the name of the event kind.
  58          */
  59         String name();
  60 
  61         /**
  62          * Returns the type of the {@link WatchEvent#context context} value.
  63          */
  64         Class<T> type();
  65     }
  66 
  67     /**
  68      * An event modifier that qualifies how a {@link Watchable} is registered
  69      * with a {@link WatchService}.
  70      *
  71      * <p> This release does not define any <em>standard</em> modifiers.
  72      *
  73      * @since 1.7
  74      * @see Watchable#register
  75      */
  76     public static interface Modifier {
  77         /**
  78          * Returns the name of the modifier.
  79          */
  80         String name();
  81     }
  82 
  83     /**
  84      * Returns the event kind.
  85      *
  86      * @return  the event kind
  87      */
  88     Kind<T> kind();
  89 
  90     /**
  91      * Returns the event count. If the event count is greater than {@code 1}
  92      * then this is a repeated event.
  93      *
  94      * @return  the event count
  95      */
  96     int count();
  97 
  98     /**
  99      * Returns the context for the event.
 100      *
 101      * <p> In the case of {@link StandardWatchEventKind#ENTRY_CREATE ENTRY_CREATE},
 102      * {@link StandardWatchEventKind#ENTRY_DELETE ENTRY_DELETE}, and {@link
 103      * StandardWatchEventKind#ENTRY_MODIFY ENTRY_MODIFY} events the context is
 104      * a {@code Path} that is the {@link Path#relativize relative} path between
 105      * the directory registered with the watch service, and the entry that is
 106      * created, deleted, or modified.
 107      *
 108      * @return  the event context; may be {@code null}
 109      */
 110     T context();
 111 }