echopointng.history.HistoryState Maven / Gradle / Ivy
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/*
* This file is part of the Echo Point Project. This project is a collection
* of Components that have extended the Echo Web Application Framework.
*
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*/
package echopointng.history;
import java.io.Serializable;
/**
* HistoryState is a interface that represents an application state at a
* given point of time.
*
* The objects that implement this interface will typically contain state
* information that allows an application to go backwards (ie undo some actions)
* and go forwards (ie redo some actions).
*
* @see echopointng.HistoryMonitor
* @see echopointng.history.HistoryEvent
* @see echopointng.history.HistoryEventListener
*/
public interface HistoryState extends Serializable {
/**
* This is a unique history hash value that can be used to uniquely identify
* this particular slice of application state. This method should follow the same semantics
* as Object.hashCode() especially in regards to how it acts when used as the
* key of a java.util.Map.
*
* The value used be will be display to the user on their browser as indication of where they are
* inside the application. Therefore there are some size contrictions on the length of this string
* which is the maximum size of a URL parameter in the users browser. To be safe use fairly compact
* strings (< 256 chars say)
*
* This is method is defined as a String to allow more meaningful state to be displayed
* and also to allow possible "encoding" of application state in the hashCode itself.
*
* The most trivial implementation fo this method would be
*
* public String historyHash() {
* return String.valueOf(this.hashCode());
* }
*
*
* A more human friendly implementation might be something like this
*
* public String historyHash() {
* return whatAreWeDoing + "-" + System.identityHashCode(new Object());
* }
*
*
* @return - a unique history hash code
*/
public String historyHash();
}