2 * Rhynodge - 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.rhynodge;
20 import net.pterodactylus.rhynodge.states.FileState;
23 * A trigger determines whether two different states actually warrant a change
24 * trigger. For example, two {@link FileState}s might contain different file
25 * sizes but a trigger might only care about whether the file appeared or
26 * disappeared since the last check.
28 * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
30 public interface Trigger {
33 * Merges the current state into the previous state, returning the merged
36 * @param previousState
37 * The previous state of the system
39 * The current state of a system
40 * @return The new state, containing a meaningful merge between the previous
41 * and the current state
43 State mergeStates(State previousState, State currentState);
46 * Checks whether the states given to {@link #mergeStates(State, State)}
47 * warrant a change trigger.
49 * @return {@code true} if the states given to
50 * {@link #mergeStates(State, State)} warrant a change trigger,
51 * {@code false} otherwise