001 /*
002 *
003 * Licensed to the Apache Software Foundation (ASF) under one
004 * or more contributor license agreements. See the NOTICE file
005 * distributed with this work for additional information
006 * regarding copyright ownership. The ASF licenses this file
007 * to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance
009 * with the License. You may obtain a copy of the License at
010 *
011 * http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing,
014 * software distributed under the License is distributed on an
015 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
016 * KIND, either express or implied. See the License for the
017 * specific language governing permissions and limitations
018 * under the License.
019 *
020 */
021 package org.apache.qpid.server.util;
022
023 import java.util.Iterator;
024
025 import org.apache.log4j.Logger;
026
027 public class CircularBuffer implements Iterable
028 {
029
030 private static final Logger _logger = Logger.getLogger(CircularBuffer.class);
031
032 private final Object[] _log;
033 private int _size;
034 private int _index;
035
036 public CircularBuffer(int size)
037 {
038 _log = new Object[size];
039 }
040
041 public void add(Object o)
042 {
043 _log[_index++] = o;
044 _size = Math.min(_size+1, _log.length);
045 if(_index >= _log.length)
046 {
047 _index = 0;
048 }
049 }
050
051 public Object get(int i)
052 {
053 if(i >= _log.length)
054 {
055 throw new ArrayIndexOutOfBoundsException(i);
056 }
057 return _log[index(i)];
058 }
059
060 public int size() {
061 return _size;
062 }
063
064 public Iterator iterator()
065 {
066 return new Iterator()
067 {
068 private int i = 0;
069
070 public boolean hasNext()
071 {
072 return i < _size;
073 }
074
075 public Object next()
076 {
077 return get(i++);
078 }
079
080 public void remove()
081 {
082 throw new UnsupportedOperationException();
083 }
084 };
085 }
086
087 public String toString()
088 {
089 StringBuilder s = new StringBuilder();
090 boolean first = true;
091 for(Object o : this)
092 {
093 if(!first)
094 {
095 s.append(", ");
096 }
097 else
098 {
099 first = false;
100 }
101 s.append(o);
102 }
103 return s.toString();
104 }
105
106 public void dump()
107 {
108 for(Object o : this)
109 {
110 _logger.info(o);
111 }
112 }
113
114 int index(int i)
115 {
116 return _size == _log.length ? (_index + i) % _log.length : i;
117 }
118
119 public static void main(String[] artgv)
120 {
121 String[] items = new String[]{
122 "A","B","C","D","E","F","G","H","I","J","K"
123 };
124 CircularBuffer buffer = new CircularBuffer(5);
125 for(String s : items)
126 {
127 buffer.add(s);
128 _logger.info(buffer);
129 }
130 }
131 }
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