org.eclipse.jgit/src/org/eclipse/jgit/util/LRUMap.java

/*
 * Copyright (C) 2018, Konrad Windszus <konrad_w@gmx.de>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - 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.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS 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 COPYRIGHT OWNER OR
 * 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.
 */
package org.eclipse.jgit.util;

import java.util.LinkedHashMap;

/**
 * Map with only up to n entries. If a new entry is added so that the map
 * contains more than those n entries the least-recently used entry is removed
 * from the map.
 *
 * @param <K>
 *            the type of keys maintained by this map
 * @param <V>
 *            the type of mapped values
 *
 * @since 5.4
 */
public class LRUMap<K, V> extends LinkedHashMap<K, V> {

	private static final long serialVersionUID = 4329609127403759486L;

	private final int limit;

	/**
	 * Constructs an empty map which may contain at most the given amount of
	 * entries.
	 *
	 * @param initialCapacity
	 *            the initial capacity
	 * @param limit
	 *            the number of entries the map should have at most
	 */
	public LRUMap(int initialCapacity, int limit) {
		super(initialCapacity, 0.75f, true);
		this.limit = limit;
	}

	@Override
	protected boolean removeEldestEntry(java.util.Map.Entry<K, V> eldest) {
		return size() > limit;
	}
}