1 /*
2 * Copyright (C) 2018, Konrad Windszus <konrad_w@gmx.de>
3 * and other copyright owners as documented in the project's IP log.
4 *
5 * This program and the accompanying materials are made available
6 * under the terms of the Eclipse Distribution License v1.0 which
7 * accompanies this distribution, is reproduced below, and is
8 * available at http://www.eclipse.org/org/documents/edl-v10.php
9 *
10 * All rights reserved.
11 *
12 * Redistribution and use in source and binary forms, with or
13 * without modification, are permitted provided that the following
14 * conditions are met:
15 *
16 * - Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 *
19 * - Redistributions in binary form must reproduce the above
20 * copyright notice, this list of conditions and the following
21 * disclaimer in the documentation and/or other materials provided
22 * with the distribution.
23 *
24 * - Neither the name of the Eclipse Foundation, Inc. nor the
25 * names of its contributors may be used to endorse or promote
26 * products derived from this software without specific prior
27 * written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
30 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
31 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
32 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
34 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
35 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
36 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
37 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
38 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
41 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
42 */
43 package org.eclipse.jgit.util;
44
45 import java.util.LinkedHashMap;
46
47 /**
48 * Map with only up to n entries. If a new entry is added so that the map
49 * contains more than those n entries the least-recently used entry is removed
50 * from the map.
51 *
52 * @param <K>
53 * the type of keys maintained by this map
54 * @param <V>
55 * the type of mapped values
56 *
57 * @since 5.4
58 */
59 public class LRUMap<K, V> extends LinkedHashMap<K, V> {
60
61 private static final long serialVersionUID = 4329609127403759486L;
62
63 private final int limit;
64
65 /**
66 * Constructs an empty map which may contain at most the given amount of
67 * entries.
68 *
69 * @param initialCapacity
70 * the initial capacity
71 * @param limit
72 * the number of entries the map should have at most
73 */
74 public LRUMap(int initialCapacity, int limit) {
75 super(initialCapacity, 0.75f, true);
76 this.limit = limit;
77 }
78
79 @Override
80 protected boolean removeEldestEntry(java.util.Map.Entry<K, V> eldest) {
81 return size() > limit;
82 }
83 }