LRUMap.java

/*
 * Copyright (C) 2018, Konrad Windszus <konrad_w@gmx.de> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */
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;
    }
}