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A set of basic utilities used in Jitsi projects

There is a newer version: 1.0-133-g6af1020

/*
 * Copyright @ 2018 - present 8x8, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jitsi.utils;

import java.util.*;

/**
 * @author George Politis
 */
public class LRUCache extends LinkedHashMap
{
    /**
     * Creates a new LRU set. For a set with insertion order
     * ({@code accessOrder = false}), only inserting new elements in the set
     * is taken into account. With access order, any insertion (even for
     * elements already in the set) "touches" them.
     * @param cacheSize the maximum number of entries.
     * @param accessOrder {@code true} to use access order, and {@code false}
     * to use insertion order.
     */
    public static Set lruSet(int cacheSize, boolean accessOrder)
    {
        return Collections.newSetFromMap(new LRUCache(cacheSize, accessOrder));
    }

    /**
     * The maximum number of entries this cache will store.
     */
    private int cacheSize;

    /**
     * Initializes a {@link LRUCache} with a given size using insertion
     * order.
     *
     * @param cacheSize the maximum number of entries.
     */
    public LRUCache(int cacheSize)
    {
        this(cacheSize, false);
    }

    /**
     * Initializes a {@link LRUCache} with a given size using either
     * insertion or access order depending on {@code accessOrder}.
     *
     * @param cacheSize the maximum number of entries.
     * @param accessOrder {@code true} to use access order, and {@code false}
     * to use insertion order.
     */
    public LRUCache(int cacheSize, boolean accessOrder)
    {
        super(16 /* DEFAULT_INITIAL_CAPACITY */,
              0.75f /* DEFAULT_LOAD_FACTOR */,
              accessOrder);
        this.cacheSize = cacheSize;
    }

    /**
     * @return the eldest item in the cache.
     */
    public Map.Entry eldest() { return this.entrySet().iterator().next(); }

    /**
     * {@inheritDoc}
     */
    @Override
    protected boolean removeEldestEntry(Map.Entry eldest)
    {
        return size() > cacheSize;
    }
}