package ca.ubc.cs.spl.aspectPatterns.examples.state.java;
/* -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* This file is part of the design patterns project at UBC
*
* 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
* either http://www.mozilla.org/MPL/ or http://aspectj.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.
*
* The Original Code is ca.ubc.cs.spl.aspectPatterns.
*
* For more details and the latest version of this code, please see:
* http://www.cs.ubc.ca/labs/spl/projects/aodps.html
*
* Contributor(s):
*/
/**
* Implements the <i>ConcreteState</i> "normal" for the queue example.
* Inserting and deleting items is possible in this state.
*
* @author Jan Hannemann
* @author Gregor Kiczales
* @version 1.1, 02/17/04
*
* @see QueueEmpty
* @see QueueFull
*/
public class QueueNormal implements QueueState {
/**
* stores the items in the queue
*/
protected Object[] items = new Object[3];
/**
* stores the index of the first item in the queue
*/
protected int first = 0;
/**
* stores the index of the last item in the queue
*/
protected int last = 0;
/**
* Creates a new QueueNormal state object with the given set of elements
* and the given indices for first and last object.
*
* @param items the content of the full queue
* @param first the index of the first item in the queue
* @param last the index of the last item in the queue
*/
public QueueNormal(Object[] items, int first, int last) {
this.items = items;
this.first = first;
this.last = last;
}
/**
* Alternate constructor that uses preset values for object variables.
*/
public QueueNormal() {
}
/**
* Tries to insert an object into the queue. Returns true if successful,
* false otherwiese. If the queue is full
* after the insertion, the state of the context is changed to "full".
*
* @param context the <i>Context</i> for this design pattern (for update
* on demand)
* @param arg the object to be inserted into the queue
* @return true if insertion was successful, false otherwise.
*/
public boolean insert(QueueContext context, Object arg) {
items[(last)%items.length] = arg;
last = (last+1) % items.length;
if (first == last) {
context.setState(new QueueFull(items, first));
}
return true;
}
/**
* Returns the first item in the queue.
*
* @param context the <i>Context</i> for this design pattern (for update
* on demand)
* @return the first item in the queue.
*/
public Object getFirst(QueueContext context) {
return items[first];
}
/**
* Tries to remove an object from the queue. Returns true if successful,
* false otherwiese. If the removed item was
* the last one in the queue, the state of the context is changed to
* "empty".
*
* @param context the <i>Context</i> for this design pattern (for update
* on demand)
* @return true if deletion was successful, false otherwise.
*/
public boolean removeFirst(QueueContext context){
first = (first + 1) % items.length;
if (first == last) {
context.setState(new QueueEmpty());
}
return true;
}
}