--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/com/go/trove/util/Cache.java	Sat Mar 21 11:00:06 2009 +0000
@@ -0,0 +1,156 @@
+/* ====================================================================
+ * Trove - Copyright (c) 1997-2000 Walt Disney Internet Group
+ * ====================================================================
+ * The Tea Software License, Version 1.1
+ *
+ * Copyright (c) 2000 Walt Disney Internet Group. 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 acknowledgment:
+ *       "This product includes software developed by the
+ *        Walt Disney Internet Group (http://opensource.go.com/)."
+ *    Alternately, this acknowledgment may appear in the software itself,
+ *    if and wherever such third-party acknowledgments normally appear.
+ *
+ * 4. The names "Tea", "TeaServlet", "Kettle", "Trove" and "BeanDoc" must
+ *    not be used to endorse or promote products derived from this
+ *    software without prior written permission. For written
+ *    permission, please contact opensource@dig.com.
+ *
+ * 5. Products derived from this software may not be called "Tea",
+ *    "TeaServlet", "Kettle" or "Trove", nor may "Tea", "TeaServlet",
+ *    "Kettle", "Trove" or "BeanDoc" appear in their name, without prior
+ *    written permission of the Walt Disney Internet 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 WALT DISNEY INTERNET GROUP 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.
+ * ====================================================================
+ *
+ * For more information about Tea, please see http://opensource.go.com/.
+ */
+
+package com.go.trove.util;
+
+import java.util.*;
+
+/******************************************************************************
+ * Cache is a SoftHashMap that is guaranteed to have the most recently used
+ * entries available. Calling "get" or "put" updates the internal MRU list,
+ * but calling "containsKey" or "containsValue" will not.
+ * <p>
+ * Like its base class, Cache is not thread-safe and must be wrapped with
+ * Collections.synchronizedMap to be made thread-safe.
+ *
+ * @author Brian S O'Neill
+ * @version
+ * <!--$$Revision: 1.1 $-->, <!--$$JustDate:--> 01/05/30 <!-- $-->
+ */
+public class Cache extends SoftHashMap {
+    private final int mMaxRecent;
+    // Contains hard references to entries.
+    private final UsageMap mUsageMap;
+
+    /**
+     * Construct a Cache with an amount of recently used entries that are
+     * guaranteed to always be in the Cache.
+     *
+     * @param maxRecent maximum amount of recently used entries guaranteed to
+     * be in the Cache.
+     * @throws IllegalArgumentException if maxRecent is less than or equal to
+     * zero.
+     */
+    public Cache(int maxRecent) {
+        if (maxRecent <= 0) {
+            throw new IllegalArgumentException
+                ("Max recent must be greater than zero: " + maxRecent);
+        }
+        mMaxRecent = maxRecent;
+        mUsageMap = new UsageMap();
+    }
+
+    /**
+     * Piggyback this Cache onto another one in order for the map of recently
+     * used entries to be shared. If this Cache is more active than the one
+     * it attaches to, then more of its most recently used entries will be
+     * guaranteed to be in the Cache, possibly bumping out entries from the
+     * other Cache.
+     */
+    public Cache(Cache cache) {
+        mMaxRecent = cache.mMaxRecent;
+        mUsageMap = cache.mUsageMap;
+    }
+
+    public Object get(Object key) {
+        Object value = super.get(key);
+        if (value != null || super.containsKey(key)) {
+            adjustMRU(key, value);
+        }
+        return value;
+    }
+
+    public Object put(Object key, Object value) {
+        if (value == null) {
+            value = new Null();
+        }
+        adjustMRU(key, value);
+        return super.put(key, value);
+    }
+
+    public Object remove(Object key) {
+        synchronized (mUsageMap) {
+            mUsageMap.remove(key);
+        }
+        return super.remove(key);
+    }
+
+    public void clear() {
+        super.clear();
+        synchronized (mUsageMap) {
+            mUsageMap.clear();
+        }
+    }
+
+    private void adjustMRU(Object key, Object value) {
+        synchronized (mUsageMap) {
+            Object existing = mUsageMap.get(key);
+            
+            if (existing != null) {
+                if (value == null && existing instanceof Null) {
+                    value = existing;
+                }
+            }
+            else {
+                if (!mUsageMap.containsKey(key)) {
+                    // A new entry will be put into the UsageMap, so remove
+                    // least recently used if MRU is too big.
+                    while (mUsageMap.size() >= mMaxRecent) {
+                        mUsageMap.remove(mUsageMap.lastKey());
+                    }
+                }
+            }
+            
+            mUsageMap.put(key, value);
+        }
+    }
+}