/*
 * Copyright 2004, 2005, 2006 Acegi Technology Pty Limited
 *
 * 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.springframework.security.acls.model;

import java.io.Serializable;

/**
 * Represents the identity of an individual domain object instance.
 *
 * <p>
 * As implementations of <tt>ObjectIdentity</tt> are used as the key to represent domain
 * objects in the ACL subsystem, it is essential that implementations provide methods so
 * that object-equality rather than reference-equality can be relied upon reliably. In
 * other words, the ACL subsystem can consider two <tt>ObjectIdentity</tt>s equal if
 * <tt>identity1.equals(identity2)</tt>, rather than reference-equality of
 * <tt>identity1==identity2</tt>.
 * </p>
 *
 * @author Ben Alex
 */
public interface ObjectIdentity extends Serializable {
	// ~ Methods
	// ========================================================================================================

	/**
	 * @param obj to be compared
	 *
	 * @return <tt>true</tt> if the objects are equal, <tt>false</tt> otherwise
	 * @see Object#equals(Object)
	 */
	boolean equals(Object obj);

	/**
	 * Obtains the actual identifier. This identifier must not be reused to represent
	 * other domain objects with the same <tt>javaType</tt>.
	 *
	 * <p>
	 * Because ACLs are largely immutable, it is strongly recommended to use a synthetic
	 * identifier (such as a database sequence number for the primary key). Do not use an
	 * identifier with business meaning, as that business meaning may change in the future
	 * such change will cascade to the ACL subsystem data.
	 * </p>
	 *
	 * @return the identifier (unique within this <tt>type</tt>; never <tt>null</tt>)
	 */
	Serializable getIdentifier();

	/**
	 * Obtains the "type" metadata for the domain object. This will often be a Java type
	 * name (an interface or a class) &ndash; traditionally it is the name of the domain
	 * object implementation class.
	 *
	 * @return the "type" of the domain object (never <tt>null</tt>).
	 */
	String getType();

	/**
	 * @return a hash code representation of the <tt>ObjectIdentity</tt>
	 * @see Object#hashCode()
	 */
	int hashCode();
}
