Source Code Cross Referenced for UnboundedFifoBuffer.java in  » Library » Apache-common-Collections » org » apache » commons » collections » buffer » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Library » Apache common Collections » org.apache.commons.collections.buffer 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         *  Copyright 2002-2006 The Apache Software Foundation
003:         *
004:         *  Licensed under the Apache License, Version 2.0 (the "License");
005:         *  you may not use this file except in compliance with the License.
006:         *  You may obtain a copy of the License at
007:         *
008:         *      http://www.apache.org/licenses/LICENSE-2.0
009:         *
010:         *  Unless required by applicable law or agreed to in writing, software
011:         *  distributed under the License is distributed on an "AS IS" BASIS,
012:         *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013:         *  See the License for the specific language governing permissions and
014:         *  limitations under the License.
015:         */
016:        package org.apache.commons.collections.buffer;
017:
018:        import java.io.IOException;
019:        import java.io.ObjectInputStream;
020:        import java.io.ObjectOutputStream;
021:        import java.io.Serializable;
022:        import java.util.AbstractCollection;
023:        import java.util.Iterator;
024:        import java.util.NoSuchElementException;
025:
026:        import org.apache.commons.collections.Buffer;
027:        import org.apache.commons.collections.BufferUnderflowException;
028:
029:        /**
030:         * UnboundedFifoBuffer is a very efficient implementation of
031:         * <code>Buffer</code> that can grow to any size.
032:         * According to performance testing, it exhibits a constant access time, but it
033:         * also outperforms ArrayList when used for the same purpose.
034:         * <p>
035:         * The removal order of an <code>UnboundedFifoBuffer</code> is based on the insertion
036:         * order; elements are removed in the same order in which they were added.
037:         * The iteration order is the same as the removal order.
038:         * <p>
039:         * The {@link #remove()} and {@link #get()} operations perform in constant time.
040:         * The {@link #add(Object)} operation performs in amortized constant time.  All
041:         * other operations perform in linear time or worse.
042:         * <p>
043:         * Note that this implementation is not synchronized.  The following can be
044:         * used to provide synchronized access to your <code>UnboundedFifoBuffer</code>:
045:         * <pre>
046:         *   Buffer fifo = BufferUtils.synchronizedBuffer(new UnboundedFifoBuffer());
047:         * </pre>
048:         * <p>
049:         * This buffer prevents null objects from being added.
050:         * <p>
051:         * This class is Serializable from Commons Collections 3.1.
052:         * 
053:         * @since Commons Collections 3.0 (previously in main package v2.1)
054:         * @version $Revision: 405927 $ $Date: 2006-05-12 23:57:03 +0100 (Fri, 12 May 2006) $
055:         *
056:         * @author Avalon
057:         * @author Federico Barbieri
058:         * @author Berin Loritsch
059:         * @author Paul Jack
060:         * @author Stephen Colebourne
061:         * @author Andreas Schlosser
062:         * @author Thomas Knych
063:         * @author Jordan Krey
064:         */
065:        public class UnboundedFifoBuffer extends AbstractCollection implements 
066:                Buffer, Serializable {
067:            // invariant: buffer.length > size()
068:            //   ie.buffer always has at least one empty entry
069:
070:            /** Serialization vesrion */
071:            private static final long serialVersionUID = -3482960336579541419L;
072:
073:            /** The array of objects in the buffer. */
074:            protected transient Object[] buffer;
075:            /** The current head index. */
076:            protected transient int head;
077:            /** The current tail index. */
078:            protected transient int tail;
079:
080:            /**
081:             * Constructs an UnboundedFifoBuffer with the default number of elements.
082:             * It is exactly the same as performing the following:
083:             *
084:             * <pre>
085:             *   new UnboundedFifoBuffer(32);
086:             * </pre>
087:             */
088:            public UnboundedFifoBuffer() {
089:                this (32);
090:            }
091:
092:            /**
093:             * Constructs an UnboundedFifoBuffer with the specified number of elements.
094:             * The integer must be a positive integer.
095:             * 
096:             * @param initialSize  the initial size of the buffer
097:             * @throws IllegalArgumentException  if the size is less than 1
098:             */
099:            public UnboundedFifoBuffer(int initialSize) {
100:                if (initialSize <= 0) {
101:                    throw new IllegalArgumentException(
102:                            "The size must be greater than 0");
103:                }
104:                buffer = new Object[initialSize + 1];
105:                head = 0;
106:                tail = 0;
107:            }
108:
109:            //-----------------------------------------------------------------------
110:            /**
111:             * Write the buffer out using a custom routine.
112:             * 
113:             * @param out  the output stream
114:             * @throws IOException
115:             */
116:            private void writeObject(ObjectOutputStream out) throws IOException {
117:                out.defaultWriteObject();
118:                out.writeInt(size());
119:                for (Iterator it = iterator(); it.hasNext();) {
120:                    out.writeObject(it.next());
121:                }
122:            }
123:
124:            /**
125:             * Read the buffer in using a custom routine.
126:             * 
127:             * @param in  the input stream
128:             * @throws IOException
129:             * @throws ClassNotFoundException
130:             */
131:            private void readObject(ObjectInputStream in) throws IOException,
132:                    ClassNotFoundException {
133:                in.defaultReadObject();
134:                int size = in.readInt();
135:                buffer = new Object[size + 1];
136:                for (int i = 0; i < size; i++) {
137:                    buffer[i] = in.readObject();
138:                }
139:                head = 0;
140:                tail = size;
141:            }
142:
143:            //-----------------------------------------------------------------------
144:            /**
145:             * Returns the number of elements stored in the buffer.
146:             *
147:             * @return this buffer's size
148:             */
149:            public int size() {
150:                int size = 0;
151:
152:                if (tail < head) {
153:                    size = buffer.length - head + tail;
154:                } else {
155:                    size = tail - head;
156:                }
157:
158:                return size;
159:            }
160:
161:            /**
162:             * Returns true if this buffer is empty; false otherwise.
163:             *
164:             * @return true if this buffer is empty
165:             */
166:            public boolean isEmpty() {
167:                return (size() == 0);
168:            }
169:
170:            /**
171:             * Adds the given element to this buffer.
172:             *
173:             * @param obj  the element to add
174:             * @return true, always
175:             * @throws NullPointerException  if the given element is null
176:             */
177:            public boolean add(final Object obj) {
178:                if (obj == null) {
179:                    throw new NullPointerException(
180:                            "Attempted to add null object to buffer");
181:                }
182:
183:                if (size() + 1 >= buffer.length) {
184:                    // copy contents to a new buffer array
185:                    Object[] tmp = new Object[((buffer.length - 1) * 2) + 1];
186:                    int j = 0;
187:                    // move head to element zero in the new array
188:                    for (int i = head; i != tail;) {
189:                        tmp[j] = buffer[i];
190:                        buffer[i] = null;
191:
192:                        j++;
193:                        i = increment(i);
194:                    }
195:                    buffer = tmp;
196:                    head = 0;
197:                    tail = j;
198:                }
199:
200:                buffer[tail] = obj;
201:                tail = increment(tail);
202:                return true;
203:            }
204:
205:            /**
206:             * Returns the next object in the buffer.
207:             *
208:             * @return the next object in the buffer
209:             * @throws BufferUnderflowException  if this buffer is empty
210:             */
211:            public Object get() {
212:                if (isEmpty()) {
213:                    throw new BufferUnderflowException(
214:                            "The buffer is already empty");
215:                }
216:
217:                return buffer[head];
218:            }
219:
220:            /**
221:             * Removes the next object from the buffer
222:             *
223:             * @return the removed object
224:             * @throws BufferUnderflowException  if this buffer is empty
225:             */
226:            public Object remove() {
227:                if (isEmpty()) {
228:                    throw new BufferUnderflowException(
229:                            "The buffer is already empty");
230:                }
231:
232:                Object element = buffer[head];
233:                if (element != null) {
234:                    buffer[head] = null;
235:                    head = increment(head);
236:                }
237:                return element;
238:            }
239:
240:            /**
241:             * Increments the internal index.
242:             * 
243:             * @param index  the index to increment
244:             * @return the updated index
245:             */
246:            private int increment(int index) {
247:                index++;
248:                if (index >= buffer.length) {
249:                    index = 0;
250:                }
251:                return index;
252:            }
253:
254:            /**
255:             * Decrements the internal index.
256:             * 
257:             * @param index  the index to decrement
258:             * @return the updated index
259:             */
260:            private int decrement(int index) {
261:                index--;
262:                if (index < 0) {
263:                    index = buffer.length - 1;
264:                }
265:                return index;
266:            }
267:
268:            /**
269:             * Returns an iterator over this buffer's elements.
270:             *
271:             * @return an iterator over this buffer's elements
272:             */
273:            public Iterator iterator() {
274:                return new Iterator() {
275:
276:                    private int index = head;
277:                    private int lastReturnedIndex = -1;
278:
279:                    public boolean hasNext() {
280:                        return index != tail;
281:
282:                    }
283:
284:                    public Object next() {
285:                        if (!hasNext()) {
286:                            throw new NoSuchElementException();
287:                        }
288:                        lastReturnedIndex = index;
289:                        index = increment(index);
290:                        return buffer[lastReturnedIndex];
291:                    }
292:
293:                    public void remove() {
294:                        if (lastReturnedIndex == -1) {
295:                            throw new IllegalStateException();
296:                        }
297:
298:                        // First element can be removed quickly
299:                        if (lastReturnedIndex == head) {
300:                            UnboundedFifoBuffer.this .remove();
301:                            lastReturnedIndex = -1;
302:                            return;
303:                        }
304:
305:                        // Other elements require us to shift the subsequent elements
306:                        int i = increment(lastReturnedIndex);
307:                        while (i != tail) {
308:                            buffer[decrement(i)] = buffer[i];
309:                            i = increment(i);
310:                        }
311:
312:                        lastReturnedIndex = -1;
313:                        tail = decrement(tail);
314:                        buffer[tail] = null;
315:                        index = decrement(index);
316:                    }
317:
318:                };
319:            }
320:
321:        }
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