1 /*
   2  * Copyright (c) 2003, 2011, 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     protected abstract V create(N name);
  43 
  44     protected abstract 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             @SuppressWarnings("unchecked")
  56             V[] temp = (V[])new Object[size];
  57             oa = temp;
  58         } else {
  59             for (int i = 0; i < oa.length; i++) {
  60                 V ob = oa[i];
  61                 if (ob == null)
  62                     continue;
  63                 if (hasName(ob, name)) {
  64                     if (i > 0)
  65                         moveToFront(oa, i);
  66                     return ob;
  67                 }
  68             }
  69         }
  70 
  71         // Create a new object
  72         V ob = create(name);
  73         oa[oa.length - 1] = ob;
  74         moveToFront(oa, oa.length - 1);
  75         return ob;
  76     }
  77 
  78 }