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 }