New buffer implementation that overwrites the oldest entry when full

from Stefano Fornari


git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/collections/trunk@131031 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/collections/CircularFifoBuffer.java

@@ -0,0 +1,134 @@
+/*
+ * $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/java/org/apache/commons/collections/Attic/CircularFifoBuffer.java,v 1.1 2003/04/26 15:10:56 scolebourne Exp $
+ * ====================================================================
+ *
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2003 The Apache Software Foundation.  All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. The end-user documentation included with the redistribution, if
+ *    any, must include the following acknowlegement:
+ *       "This product includes software developed by the
+ *        Apache Software Foundation (http://www.apache.org/)."
+ *    Alternately, this acknowlegement may appear in the software itself,
+ *    if and wherever such third-party acknowlegements normally appear.
+ *
+ * 4. The names "The Jakarta Project", "Commons", and "Apache Software
+ *    Foundation" must not be used to endorse or promote products derived
+ *    from this software without prior written permission. For written
+ *    permission, please contact apache@apache.org.
+ *
+ * 5. Products derived from this software may not be called "Apache"
+ *    nor may "Apache" appear in their names without prior written
+ *    permission of the Apache Group.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.commons.collections;
+
+import java.util.Collection;
+
+import org.apache.commons.collections.BoundedFifoBuffer;
+
+/** 
+ * CircularFifoBuffer is a first in first out buffer with a fixed size that
+ * replaces its oldest element if full.
+ * <p>
+ * The removal order of a <code>CircularFifoBuffer</code> is based on the 
+ * insertion order; elements are removed in the same order in which they
+ * were added.  The iteration order is the same as the removal order.
+ * <p>
+ * The {@link #add(Object)}, {@link #remove()} and {@link #get()} operations
+ * all perform in constant time.  All other operations perform in linear
+ * time or worse.
+ * <p>
+ * Note that this implementation is not synchronized.  The following can be
+ * used to provide synchronized access to your <code>CircularFifoBuffer</code>:
+ * <pre>
+ *   Buffer fifo = BufferUtils.synchronizedBuffer(new CircularFifoBuffer());
+ * </pre>
+ * <p>
+ * This buffer prevents null objects from being added.
+ * 
+ * @since Commons Collections 2.2
+ * @version $Revision: 1.1 $ $Date: 2003/04/26 15:10:56 $
+ * 
+ * @author Stefano Fornari
+ * @author Stephen Colebourne
+ */
+public class CircularFifoBuffer extends BoundedFifoBuffer {
+
+    /**
+     * Constructor that creates a buffer with the default size of 32.
+     */
+    public CircularFifoBuffer() {
+        super(32);
+    }
+
+    /**
+     * Constructor that creates a buffer with the specified size.
+     * 
+     * @param size  the size of the buffer (cannot be changed)
+     * @throws IllegalArgumentException  if the size is less than 1
+     */
+    public CircularFifoBuffer(int size) {
+        super(size);
+    }
+
+    /**
+     * Constructor that creates a buffer from the specified collection.
+     * The collection size also sets the buffer size
+     * 
+     * @param coll  the collection to copy into the buffer, may not be null
+     * @throws NullPointerException if the collection is null
+     */
+    public CircularFifoBuffer(Collection coll) {
+        super(coll);
+    }
+
+    /**
+     * If the buffer is full, the least recently added element is discarded so
+     * that a new element can be inserted.
+     *
+     * @param element the element to add
+     * @return true, always
+     */
+    public boolean add(Object element) {
+        if (isFull()) {
+            remove();
+        }
+        return super.add(element);
+    }
+    
+}