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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;

/**
 * Interface for cache backends. This is a basic key-based get/set interface. However, we do not use
 * the method names from the map interface, as we do not have map semantics (i.e. information can
 * get lost).
 * 
 * Implementations are not required to deal with synchronization. This has to be handled by the
 * caller.
 * 
 * @param 
 *            the key type. This must have both {@link Object#equals(Object)} and
 *            {@link Object#hashCode()} correctly implemented.
 * 
 * @param 
 *            the value type. It is generally recommended to use an immutable type here, but this is
 *            not required.
 */
public interface ICacheBackend {

	/** Stores an element (value) using the given key. */
	void store(K key, V value);

	/**
	 * Returns the value stored at a given key or null. The cache guarantees, that only values inserted
	 * via {@link #store(Object, Object)} can be returned. However, there is no guarantee that a
	 * non-null value is returned, i.e. the cache may forget information.
	 */
	V retrieve(K key);

	/**
	 * Returns a new instance of this backend. This is required as certain cache implementations require
	 * multiple backends, and cloning is not an option as we do not want to duplicate the cache
	 * contents.
	 */
	ICacheBackend newInstance();
}