From a8b6683bc4f91b409fd3ca2b21d92ef86ddd5baf Mon Sep 17 00:00:00 2001
From: =?utf8?q?David=20=E2=80=98Bombe=E2=80=99=20Roden?=
 <bombe@pterodactylus.net>
Date: Wed, 2 Jan 2013 02:36:47 +0100
Subject: [PATCH] Add trigger interface.

---
 .../java/net/pterodactylus/reactor/Trigger.java    | 46 ++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 src/main/java/net/pterodactylus/reactor/Trigger.java

diff --git a/src/main/java/net/pterodactylus/reactor/Trigger.java b/src/main/java/net/pterodactylus/reactor/Trigger.java
new file mode 100644
index 0000000..449b4fe
--- /dev/null
+++ b/src/main/java/net/pterodactylus/reactor/Trigger.java
@@ -0,0 +1,46 @@
+/*
+ * Reactor - Trigger.java - Copyright © 2013 David Roden
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.pterodactylus.reactor;
+
+import net.pterodactylus.reactor.states.FileState;
+
+/**
+ * A trigger determines whether two different states actually warrant a change
+ * trigger. For example, two {@link FileState}s might contain different file
+ * sizes but a trigger might only care about whether the file appeared or
+ * disappeared since the last check.
+ *
+ * @param <S>
+ *            The type of the state
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public interface Trigger<S extends State> {
+
+	/**
+	 * Checks whether the given states warrant a change trigger.
+	 *
+	 * @param currentState
+	 *            The current state of a system
+	 * @param previousState
+	 *            The previous state of the system
+	 * @return {@code true} if the given states warrant a change trigger,
+	 *         {@code false} otherwise
+	 */
+	boolean triggers(S currentState, S previousState);
+
+}
-- 
2.7.4