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    1   /*
    2    * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package sun.misc;
   27   
   28   /**
   29    * Utility class for small LRU caches.
   30    *
   31    * @author Mark Reinhold
   32    */
   33   public abstract class LRUCache<N,V> {
   34   
   35       private V[] oa = null;
   36       private final int size;
   37   
   38       public LRUCache(int size) {
   39           this.size = size;
   40       }
   41   
   42       abstract protected V create(N name);
   43   
   44       abstract protected boolean hasName(V ob, N name);
   45   
   46       public static void moveToFront(Object[] oa, int i) {
   47           Object ob = oa[i];
   48           for (int j = i; j > 0; j--)
   49               oa[j] = oa[j - 1];
   50           oa[0] = ob;
   51       }
   52   
   53       public V forName(N name) {
   54           if (oa == null) {
   55               oa = (V[])new Object[size];
   56           } else {
   57               for (int i = 0; i < oa.length; i++) {
   58                   V ob = oa[i];
   59                   if (ob == null)
   60                       continue;
   61                   if (hasName(ob, name)) {
   62                       if (i > 0)
   63                           moveToFront(oa, i);
   64                       return ob;
   65                   }
   66               }
   67           }
   68   
   69           // Create a new object
   70           V ob = create(name);
   71           oa[oa.length - 1] = ob;
   72           moveToFront(oa, oa.length - 1);
   73           return ob;
   74       }
   75   
   76   }

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