001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one or more
003     *  contributor license agreements.  See the NOTICE file distributed with
004     *  this work for additional information regarding copyright ownership.
005     *  The ASF licenses this file to You under the Apache License, Version 2.0
006     *  (the "License"); you may not use this file except in compliance with
007     *  the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     *  Unless required by applicable law or agreed to in writing, software
012     *  distributed under the License is distributed on an "AS IS" BASIS,
013     *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     *  See the License for the specific language governing permissions and
015     *  limitations under the License.
016     */
017    package org.apache.commons.collections.buffer;
018    
019    import java.util.Collection;
020    
021    /** 
022     * CircularFifoBuffer is a first in first out buffer with a fixed size that
023     * replaces its oldest element if full.
024     * <p>
025     * The removal order of a <code>CircularFifoBuffer</code> is based on the 
026     * insertion order; elements are removed in the same order in which they
027     * were added.  The iteration order is the same as the removal order.
028     * <p>
029     * The {@link #add(Object)}, {@link #remove()} and {@link #get()} operations
030     * all perform in constant time.  All other operations perform in linear
031     * time or worse.
032     * <p>
033     * Note that this implementation is not synchronized.  The following can be
034     * used to provide synchronized access to your <code>CircularFifoBuffer</code>:
035     * <pre>
036     *   Buffer fifo = BufferUtils.synchronizedBuffer(new CircularFifoBuffer());
037     * </pre>
038     * <p>
039     * This buffer prevents null objects from being added.
040     * <p>
041     * This class is Serializable from Commons Collections 3.1.
042     * 
043     * @since Commons Collections 3.0
044     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
045     * 
046     * @author Stefano Fornari
047     * @author Stephen Colebourne
048     */
049    public class CircularFifoBuffer extends BoundedFifoBuffer {
050    
051        /** Serialization version */
052        private static final long serialVersionUID = -8423413834657610406L;
053    
054        /**
055         * Constructor that creates a buffer with the default size of 32.
056         */
057        public CircularFifoBuffer() {
058            super(32);
059        }
060    
061        /**
062         * Constructor that creates a buffer with the specified size.
063         * 
064         * @param size  the size of the buffer (cannot be changed)
065         * @throws IllegalArgumentException  if the size is less than 1
066         */
067        public CircularFifoBuffer(int size) {
068            super(size);
069        }
070    
071        /**
072         * Constructor that creates a buffer from the specified collection.
073         * The collection size also sets the buffer size
074         * 
075         * @param coll  the collection to copy into the buffer, may not be null
076         * @throws NullPointerException if the collection is null
077         */
078        public CircularFifoBuffer(Collection coll) {
079            super(coll);
080        }
081    
082        /**
083         * If the buffer is full, the least recently added element is discarded so
084         * that a new element can be inserted.
085         *
086         * @param element the element to add
087         * @return true, always
088         */
089        public boolean add(Object element) {
090            if (isFull()) {
091                remove();
092            }
093            return super.add(element);
094        }
095        
096    }