Reference.java

/**
 * Copyright 2011-2012 Universite Joseph Fourier, LIG, ADELE team
 *   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 fr.imag.adele.apam.declarations.references;

/**
 * This class represents a reference to an externally defined entity. This
 * allows self-contained declarations that only indirectly reference other
 * entities.
 * 
 * References are organized in namespaces, and are always completely qualified
 * so that they can be used as identifiers.
 * 
 * 
 * @author vega
 * 
 */
public abstract class Reference {

	/**
	 * A class to represent different namespaces.
	 * 
	 * Notice that namespaces must be unique objects, this is not verified but
	 * must be enforced by concrete subclasses of this base class.
	 */
	public interface Namespace {

	}

	/**
	 * The namespace associated to the identifier
	 */
	protected final Namespace namespace;

	/**
	 * Default constructor
	 */
	protected Reference(Namespace namespace) {

		assert namespace != null;
		this.namespace = namespace;
	}

	/**
	 * Cast this reference to a more specific class of references.
	 * 
	 * Returns null if the cast is not possible
	 */
	@SuppressWarnings("unchecked")
	public <R extends Reference> R as(Class<R> kind) {

		if (kind.isAssignableFrom(this.getClass())) {
			return (R) this;
		}

		return null;
	}

	/**
	 * Resources are uniquely identified by identifier and namespace.
	 * 
	 */
	@Override
	public final boolean equals(Object object) {
		if (this == object) {
			return true;
		}

		if (!(object instanceof Reference)) {
			return false;
		}

		Reference that = (Reference) object;
		return this.namespace.equals(that.namespace)
				&& this.getIdentifier().equals(that.getIdentifier());
	}

	/**
	 * The identifier of the referenced resource
	 */
	public abstract String getIdentifier();

	/**
	 * Hash code is based on identity
	 */
	@Override
	public final int hashCode() {
		return namespace.hashCode() + getIdentifier().hashCode();
	}

}