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;
018    
019    import java.util.Collection;
020    
021    /**
022     * Defines a collection that allows objects to be removed in some well-defined order.
023     * <p>
024     * The removal order can be based on insertion order (eg, a FIFO queue or a
025     * LIFO stack), on access order (eg, an LRU cache), on some arbitrary comparator
026     * (eg, a priority queue) or on any other well-defined ordering.
027     * <p>
028     * Note that the removal order is not necessarily the same as the iteration
029     * order.  A <code>Buffer</code> implementation may have equivalent removal
030     * and iteration orders, but this is not required.
031     * <p>
032     * This interface does not specify any behavior for 
033     * {@link Object#equals(Object)} and {@link Object#hashCode} methods.  It
034     * is therefore possible for a <code>Buffer</code> implementation to also
035     * also implement {@link java.util.List}, {@link java.util.Set} or 
036     * {@link Bag}.
037     *
038     * @since Commons Collections 2.1
039     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
040     * 
041     * @author Avalon
042     * @author Berin Loritsch
043     * @author Paul Jack
044     * @author Stephen Colebourne
045     */
046    public interface Buffer extends Collection {
047    
048        /**
049         * Gets and removes the next object from the buffer.
050         *
051         * @return the next object in the buffer, which is also removed
052         * @throws BufferUnderflowException if the buffer is already empty
053         */
054        Object remove();
055    
056        /**
057         * Gets the next object from the buffer without removing it.
058         *
059         * @return the next object in the buffer, which is not removed
060         * @throws BufferUnderflowException if the buffer is empty
061         */
062        Object get();
063    
064    }