Java tutorial
/* * Copyright (c) 1999, 2004, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.naming; import java.util.Enumeration; /** * This interface is for enumerating lists returned by * methods in the javax.naming and javax.naming.directory packages. * It extends Enumeration to allow as exceptions to be thrown during * the enumeration. *<p> * When a method such as list(), listBindings(), or search() returns * a NamingEnumeration, any exceptions encountered are reserved until * all results have been returned. At the end of the enumeration, the * exception is thrown (by hasMore()); * <p> * For example, if the list() is * returning only a partial answer, the corresponding exception would * be PartialResultException. list() would first return a NamingEnumeration. * When the last of the results has been returned by the NamingEnumeration's * next(), invoking hasMore() would result in PartialResultException being thrown. *<p> * In another example, if a search() method was invoked with a specified * size limit of 'n'. If the answer consists of more than 'n' results, * search() would first return a NamingEnumeration. * When the n'th result has been returned by invoking next() on the * NamingEnumeration, a SizeLimitExceedException would then thrown when * hasMore() is invoked. *<p> * Note that if the program uses hasMoreElements() and nextElement() instead * to iterate through the NamingEnumeration, because these methods * cannot throw exceptions, no exception will be thrown. Instead, * in the previous example, after the n'th result has been returned by * nextElement(), invoking hasMoreElements() would return false. *<p> * Note also that NoSuchElementException is thrown if the program invokes * next() or nextElement() when there are no elements left in the enumeration. * The program can always avoid this exception by using hasMore() and * hasMoreElements() to check whether the end of the enumeration has been reached. *<p> * If an exception is thrown during an enumeration, * the enumeration becomes invalid. * Subsequent invocation of any method on that enumeration * will yield undefined results. * * @author Rosanna Lee * @author Scott Seligman * * @see Context#list * @see Context#listBindings * @see javax.naming.directory.DirContext#search * @see javax.naming.directory.Attributes#getAll * @see javax.naming.directory.Attributes#getIDs * @see javax.naming.directory.Attribute#getAll * @since 1.3 */ public interface NamingEnumeration<T> extends Enumeration<T> { /** * Retrieves the next element in the enumeration. * This method allows naming exceptions encountered while * retrieving the next element to be caught and handled * by the application. * <p> * Note that {@code next()} can also throw the runtime exception * NoSuchElementException to indicate that the caller is * attempting to enumerate beyond the end of the enumeration. * This is different from a NamingException, which indicates * that there was a problem in obtaining the next element, * for example, due to a referral or server unavailability, etc. * * @return The possibly null element in the enumeration. * null is only valid for enumerations that can return * null (e.g. Attribute.getAll() returns an enumeration of * attribute values, and an attribute value can be null). * @exception NamingException If a naming exception is encountered while attempting * to retrieve the next element. See NamingException * and its subclasses for the possible naming exceptions. * @exception java.util.NoSuchElementException If attempting to get the next element when none is available. * @see java.util.Enumeration#nextElement */ public T next() throws NamingException; /** * Determines whether there are any more elements in the enumeration. * This method allows naming exceptions encountered while * determining whether there are more elements to be caught and handled * by the application. * * @return true if there is more in the enumeration ; false otherwise. * @exception NamingException * If a naming exception is encountered while attempting * to determine whether there is another element * in the enumeration. See NamingException * and its subclasses for the possible naming exceptions. * @see java.util.Enumeration#hasMoreElements */ public boolean hasMore() throws NamingException; /** * Closes this enumeration. * * After this method has been invoked on this enumeration, the * enumeration becomes invalid and subsequent invocation of any of * its methods will yield undefined results. * This method is intended for aborting an enumeration to free up resources. * If an enumeration proceeds to the end--that is, until * {@code hasMoreElements()} or {@code hasMore()} returns {@code false}-- * resources will be freed up automatically and there is no need to * explicitly call {@code close()}. *<p> * This method indicates to the service provider that it is free * to release resources associated with the enumeration, and can * notify servers to cancel any outstanding requests. The {@code close()} * method is a hint to implementations for managing their resources. * Implementations are encouraged to use appropriate algorithms to * manage their resources when client omits the {@code close()} calls. * * @exception NamingException If a naming exception is encountered * while closing the enumeration. * @since 1.3 */ public void close() throws NamingException; }