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jBasics is a collection of useful utility classes for Java. This includes helper for XML, mathematic functions, restful web services helper, pattern oriented programming interfaces and more. Currently Java7 and up is supported. Version 1.0 will required at leaset Java8.

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/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * 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
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.discover;

import org.jbasics.checker.ContractCheck;
import org.jbasics.pattern.delegation.ReleasableDelegate;

import java.io.Serializable;

public class DiscoverableImplementationDelegate implements ReleasableDelegate, Serializable {
	private static final long serialVersionUID = 20120101L;
	private final Class abstractClass;
	private final Class defaultImpl;
	private transient T instance;

	protected DiscoverableImplementationDelegate(final Class abstractClass, final Class defaultImpl) {
		this.abstractClass = ContractCheck.mustNotBeNull(abstractClass, "abstractClass");
		this.defaultImpl = defaultImpl;
	}

	public static  DiscoverableImplementationDelegate newInstance(final Class abstractClass) {
		return new DiscoverableImplementationDelegate(abstractClass, null);
	}

	public static  DiscoverableImplementationDelegate newInstance(final Class abstractClass, final Class defaultImpl) {
		return new DiscoverableImplementationDelegate(abstractClass, defaultImpl);
	}

	public T delegate() {
		if (this.instance == null) {
			final Class temp = ServiceClassDiscovery.discoverImplementation(this.abstractClass, this.defaultImpl);
			if (temp == null) {
				throw new RuntimeException("Cannot find an implementation for the abstract class " + this.abstractClass.getName()); //$NON-NLS-1$
			}
			try {
				this.instance = temp.newInstance();
			} catch (final InstantiationException e) {
				throw new RuntimeException("Cannot instantiate implmentation " + temp.getName(), e); //$NON-NLS-1$
			} catch (final IllegalAccessException e) {
				throw new RuntimeException("Cannot instantiate implmentation " + temp.getName(), e); //$NON-NLS-1$
			}
		}
		return this.instance;
	}

	public boolean release() {
		this.instance = null;
		return false;
	}
}