2 * Reactor - Trigger.java - Copyright © 2013 David Roden
4 * This program is free software: you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation, either version 3 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program. If not, see <http://www.gnu.org/licenses/>.
18 package net.pterodactylus.reactor;
20 import net.pterodactylus.reactor.output.Output;
21 import net.pterodactylus.reactor.states.FileState;
24 * A trigger determines whether two different states actually warrant a change
25 * trigger. For example, two {@link FileState}s might contain different file
26 * sizes but a trigger might only care about whether the file appeared or
27 * disappeared since the last check.
29 * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
31 public interface Trigger {
34 * Checks whether the given states warrant a change trigger.
37 * The current state of a system
38 * @param previousState
39 * The previous state of the system
40 * @return {@code true} if the given states warrant a change trigger,
41 * {@code false} otherwise
43 boolean triggers(State currentState, State previousState);
46 * Returns the output of this trigger. This will only return a meaningful
47 * value if {@link #triggers(State, State)} returns {@code true}.
49 * @return The output of this trigger