Add state interface.

diff --git a/src/main/java/net/pterodactylus/reactor/State.java b/src/main/java/net/pterodactylus/reactor/State.java
new file mode 100644 (file)
index 0000000..9e2face
--- /dev/null
+++ b/src/main/java/net/pterodactylus/reactor/State.java
@@ -0,0 +1,50 @@
+/*
+ * Reactor - State.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;
+
+/**
+ * Defines the current state of a system.
+ *
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public interface State {
+
+       /**
+        * Whether the state was successfully retrieved. This method should only
+        * return {@code true} if a meaningful result could be retrieved; if e. g. a
+        * service is currently not reachable, this method should return false
+        * instead of emulating success by using empty lists or similar constructs.
+        *
+        * @return {@code true} if the state could be retrieved successfully,
+        *         {@code false} otherwise
+        */
+       boolean success();
+
+       /**
+        * If {@link #success()} returns {@code false}, this method may return a
+        * {@link Throwable} to give some details for the reason why retrieving the
+        * state was not possible. For example, network-based {@link Query}s might
+        * return any exception that were encountered while communicating with the
+        * remote service.
+        *
+        * @return An exception that occured, may be {@code null} in case an
+        *         exception can not be meaningfully returned
+        */
+       Throwable exception();
+
+}