KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > smtphandler > CyclicBuffer


1 /*
2  * ============================================================================
3  * The Apache Software License, Version 1.1
4  * ============================================================================
5  *
6  * Copyright (C) 1999 The Apache Software Foundation. All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without modifica-
9  * tion, are permitted provided that the following conditions are met: 1.
10  * Redistributions of source code must retain the above copyright notice, this
11  * list of conditions and the following disclaimer. 2. Redistributions in
12  * binary form must reproduce the above copyright notice, this list of
13  * conditions and the following disclaimer in the documentation and/or other
14  * materials provided with the distribution. 3. The end-user documentation
15  * included with the redistribution, if any, must include the following
16  * acknowledgment: "This product includes software developed by the Apache
17  * Software Foundation (http://www.apache.org/)." Alternately, this
18  * acknowledgment may appear in the software itself, if and wherever such
19  * third-party acknowledgments normally appear. 4. The names "log4j" and
20  * "Apache Software Foundation" must not be used to endorse or promote products
21  * derived from this software without prior written permission. For written
22  * permission, please contact apache@apache.org. 5. Products derived from this
23  * software may not be called "Apache", nor may "Apache" appear in their name,
24  * without prior written permission of the Apache Software Foundation.
25  *
26  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
27  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
28  * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
29  * APACHE SOFTWARE FOUNDATION OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
30  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLU-
31  * DING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
32  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
33  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36  *
37  * This software consists of voluntary contributions made by many individuals
38  * on behalf of the Apache Software Foundation. For more information on the
39  * Apache Software Foundation, please see <http://www.apache.org/> .
40  *
41  */
42
43 package smtphandler;
44
45 import java.util.logging.LogRecord JavaDoc;
46
47 /**
48  *
49  * CyclicBuffer is used by other handlers to hold {@link LogRecord} objects for
50  * immediate or differed display.
51  *
52  * <p>
53  * This buffer gives read access to any element in the buffer not just the
54  * first or last element.
55  *
56  * @author Ceki G&uuml;lc&uuml;
57  * @author Sean C. Sullivan
58  *
59  */
60 public class CyclicBuffer
61 {
62     private LogRecord JavaDoc[] records;
63     private int first;
64     private int last;
65     private int numElems;
66     private int maxSize;
67
68     /**
69      * Instantiate a new CyclicBuffer of at most <code>maxSize</code>
70      * records.
71      *
72      * The <code>maxSize</code> argument must a positive integer.
73      *
74      * @param maxSize
75      * The maximum number of elements in the buffer.
76      */
77     public CyclicBuffer(int maxSize) throws IllegalArgumentException JavaDoc
78     {
79         if (maxSize < 1)
80         {
81             throw new IllegalArgumentException JavaDoc(
82                 "The maxSize argument ("
83                     + maxSize
84                     + ") is not a positive integer.");
85         }
86         this.maxSize = maxSize;
87         records = new LogRecord JavaDoc[maxSize];
88         first = 0;
89         last = 0;
90         numElems = 0;
91     }
92
93     /**
94      * Add a <code>record</code> as the last record in the buffer.
95      *
96      * @param record must be non-null
97      *
98      */
99     public void add(LogRecord JavaDoc record)
100     {
101         records[last] = record;
102         if (++last == maxSize)
103             last = 0;
104
105         if (numElems < maxSize)
106             numElems++;
107         else if (++first == maxSize)
108             first = 0;
109     }
110
111     /**
112      * Get the <i>i</i> th oldest record currently in the buffer. If <em>i</em>
113      * is outside the range 0 to the number of elements currently in the
114      * buffer, then <code>null</code> is returned.
115      *
116      * @return may return null
117      *
118      */
119     public LogRecord JavaDoc get(int i)
120     {
121         if (i < 0 || i >= numElems)
122             return null;
123
124         return records[(first + i) % maxSize];
125     }
126
127     public int getMaxSize()
128     {
129         return maxSize;
130     }
131
132     /**
133      * Get the oldest (first) element in the buffer. The oldest element is
134      * removed from the buffer.
135      *
136      * @return may return null
137      *
138      */
139     public LogRecord JavaDoc get()
140     {
141         LogRecord JavaDoc r = null;
142         if (numElems > 0)
143         {
144             numElems--;
145             r = records[first];
146             records[first] = null;
147             if (++first == maxSize)
148                 first = 0;
149         }
150         return r;
151     }
152
153     /**
154      * Get the number of elements in the buffer. This number is guaranteed to
155      * be in the range 0 to <code>maxSize</code> (inclusive).
156      */
157     public int length()
158     {
159         return numElems;
160     }
161
162     /**
163      * Resize the cyclic buffer to <code>newSize</code>.
164      *
165      * @throws IllegalArgumentException
166      * if <code>newSize</code> is negative.
167      */
168     public void resize(int newSize)
169     {
170         if (newSize < 0)
171         {
172             throw new IllegalArgumentException JavaDoc(
173                 "Negative array size [" + newSize + "] not allowed.");
174         }
175         if (newSize == numElems)
176         {
177             return; // nothing to do
178 }
179         
180         LogRecord JavaDoc[] temp = new LogRecord JavaDoc[newSize];
181
182         int loopLen = newSize < numElems ? newSize : numElems;
183
184         for (int i = 0; i < loopLen; i++)
185         {
186             temp[i] = records[first];
187             records[first] = null;
188             if (++first == numElems)
189                 first = 0;
190         }
191         records = temp;
192         first = 0;
193         numElems = loopLen;
194         maxSize = newSize;
195         if (loopLen == newSize)
196         {
197             last = 0;
198         }
199         else
200         {
201             last = loopLen;
202         }
203     }
204     
205     public String JavaDoc toString()
206     {
207         StringBuffer JavaDoc sb = new StringBuffer JavaDoc();
208         sb.append("length=" + length());
209         return sb.toString();
210     }
211 }
212
Popular Tags