/*-
 * ============LICENSE_START=======================================================
 * SDC
 * ================================================================================
 * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * 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.
 * ============LICENSE_END=========================================================
 */
package org.openecomp.core.factory.api;

import org.openecomp.core.factory.impl.AbstractFactoryBase;

/**
 * This class provides generic implementation of an abstract factory. Components exposed as Java interfaces should have their own concrete factories
 * derived from the given class. This assures code alignment and consistency across all Service Management components. The class actually uses
 * singleton pattern to instantiate and reuse just one instance of a factory. Therefore, each factory implementation has to be <i>thread-safe</i>. In
 * a general case, the hierarchy of factory objects for an Java interface <tt>IUknown</tt> may look as follows:
 * <pre>
 *                     AbstractFactory&lt;IUnknown&gt;
 *                                ^
 *                                |
 *   Application code ----> ConcreteFactory
 *                                ^
 *                                |
 *                      +---------+---------+
 *                      |                   |
 *             BaselineFactoryImpl   CustomFactoryImpl
 * </pre>
 * Where the classes responsibility is: <ul> <li>Abstract factory - common logic to retrieve the implementation class name from a central
 * repository.</li> <li>Concrete factory - abstract class that only exposes to application layer the type specific API such as: <ul> <li><tt>public
 * static ConcreteFactory getInstance()</tt></li> </ul> <li>Baseline factory - out of the box implementation of concrete factory (that can be replaced
 * by a custom one depending on customer needs) which actually implements method: <ul> <li><tt>public IUnknown createInterface()</tt></li>
 * </ul> </ul> The normal concrete factory class may look like:
 * <pre>
 * public abstract class ConcreteFactory extends AbstractFactory&lt;IUnknown&gt; {
 *   static {
 *     registerFactory(ConcreteFactory.class, BaselineFactoryImpl.class);
 *   }
 *   public static ConcreteFactory getInstance() {
 * return AbstractFactory.&lt;IUnknown, ConcreteFactory.class&gt;getInstance(ConcreteFactory.class);
 *   }
 * }
 * </pre>
 *
 * @param <I> Java interface type created by the factory.
 */
public abstract class AbstractFactory<I> extends AbstractFactoryBase {

    /**
     * Returns the interface implementor instance.
     * <b>Note</b>: It's up to the concrete factory to decide on the actual
     * implementation of the returned interface. Therefore, the call can get the same instance per each call in case of singleton implementation or
     * new instance otherwise. However, the API consumer may not assume anything regarding the underlying logic and has always go through the factory
     * to obtain the reference.
     *
     * @return Implementor of the exposed Java interface.
     */
    public abstract I createInterface();
} // End of class