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Provides common utility functions

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/*
 * Copyright (c) CQSE GmbH
 *
 * 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.conqat.lib.commons.cache4j.backend;

import java.util.LinkedHashMap;

import org.conqat.lib.commons.assertion.CCSMAssert;

/**
 * Backend implementing LRU strategy.
 */
/* package */class LRUCacheBackend implements ICacheBackend {

	/** The actual cache. */
	private final LinkedHashMap cache;

	/** Max size of the cache. */
	private final int maxCacheSize;

	/** Constructor. */
	@SuppressWarnings("serial")
	public LRUCacheBackend(int maxSize) {
		CCSMAssert.isTrue(maxSize > 0, "Maximal size must be positive!");

		maxCacheSize = maxSize;

		cache = new LinkedHashMap(2 * maxSize, .6F, true) {

			@Override
			protected boolean removeEldestEntry(java.util.Map.Entry eldest) {
				return size() > maxCacheSize;
			}
		};
	}

	/** {@inheritDoc} */
	@Override
	public void store(K key, V value) {
		cache.put(key, value);
	}

	/** {@inheritDoc} */
	@Override
	public V retrieve(K key) {
		return cache.get(key);
	}

	/** {@inheritDoc} */
	@Override
	public LRUCacheBackend newInstance() {
		return new LRUCacheBackend<>(maxCacheSize);
	}
}