MRUMapCache.java

/*
 * This file is part of Sponge, licensed under the MIT License (MIT).
 *
 * Copyright (c) SpongePowered <https://www.spongepowered.org>
 * Copyright (c) contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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 * THE SOFTWARE.
 */
package co.aikar.util;

import java.util.AbstractMap;
import java.util.Collection;
import java.util.Map;
import java.util.Set;

/**
 * Implements a Most Recently Used cache in front of a backing map, to quickly
 * access the last accessed result.
 *
 * @param <K>
 * @param <V>
 */
public class MRUMapCache<K, V> extends AbstractMap<K, V> {

    final Map<K, V> backingMap;
    Object cacheKey;
    V cacheValue;

    public MRUMapCache(final Map<K, V> backingMap) {
        this.backingMap = backingMap;
    }

    @Override
    public int size() {
        return this.backingMap.size();
    }

    @Override
    public boolean isEmpty() {
        return this.backingMap.isEmpty();
    }

    @Override
    public boolean containsKey(Object key) {
        return key != null && key.equals(this.cacheKey) || this.backingMap.containsKey(key);
    }

    @Override
    public boolean containsValue(Object value) {
        return value != null && value == this.cacheValue || this.backingMap.containsValue(value);
    }

    @Override
    public V get(Object key) {
        if (this.cacheKey != null && this.cacheKey.equals(key)) {
            return this.cacheValue;
        }
        this.cacheKey = key;
        return this.cacheValue = this.backingMap.get(key);
    }

    @Override
    public V put(K key, V value) {
        this.cacheKey = key;
        return this.cacheValue = this.backingMap.put(key, value);
    }

    @Override
    public V remove(Object key) {
        if (key != null && key.equals(this.cacheKey)) {
            this.cacheKey = null;
        }
        return this.backingMap.remove(key);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> m) {
        this.backingMap.putAll(m);
    }

    @Override
    public void clear() {
        this.cacheKey = null;
        this.cacheValue = null;
        this.backingMap.clear();
    }

    @Override
    public Set<K> keySet() {
        return this.backingMap.keySet();
    }

    @Override
    public Collection<V> values() {
        return this.backingMap.values();
    }

    @Override
    public Set<Map.Entry<K, V>> entrySet() {
        return this.backingMap.entrySet();
    }

    /**
     * Wraps the specified map with a most recently used cache
     *
     * @param map
     * @param <K>
     * @param <V>
     * @return
     */
    public static <K, V> Map<K, V> of(Map<K, V> map) {
        return new MRUMapCache<>(map);
    }

}