128 lines
5.0 KiB
Java
128 lines
5.0 KiB
Java
/*
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* Copyright (c) 1994, 2020, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.util;
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/**
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* An object that implements the Enumeration interface generates a
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* series of elements, one at a time. Successive calls to the
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* {@code nextElement} method return successive elements of the
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* series.
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* <p>
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* For example, to print all elements of a {@code Vector<E>} <i>v</i>:
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* <pre>
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* for (Enumeration<E> e = v.elements(); e.hasMoreElements();)
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* System.out.println(e.nextElement());</pre>
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* <p>
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* Methods are provided to enumerate through the elements of a
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* vector, the keys of a hashtable, and the values in a hashtable.
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* Enumerations are also used to specify the input streams to a
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* {@code SequenceInputStream}.
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*
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* @apiNote
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* The functionality of this interface is duplicated by the {@link Iterator}
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* interface. In addition, {@code Iterator} adds an optional remove operation,
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* and has shorter method names. New implementations should consider using
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* {@code Iterator} in preference to {@code Enumeration}. It is possible to
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* adapt an {@code Enumeration} to an {@code Iterator} by using the
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* {@link #asIterator} method.
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*
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* @see java.util.Iterator
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* @see java.io.SequenceInputStream
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* @see java.util.Enumeration#nextElement()
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* @see java.util.Hashtable
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* @see java.util.Hashtable#elements()
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* @see java.util.Hashtable#keys()
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* @see java.util.Vector
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* @see java.util.Vector#elements()
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*
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* @author Lee Boynton
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* @since 1.0
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*/
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public interface Enumeration<E> {
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/**
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* Tests if this enumeration contains more elements.
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*
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* @return {@code true} if and only if this enumeration object
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* contains at least one more element to provide;
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* {@code false} otherwise.
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*/
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boolean hasMoreElements();
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/**
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* Returns the next element of this enumeration if this enumeration
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* object has at least one more element to provide.
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*
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* @return the next element of this enumeration.
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* @throws NoSuchElementException if no more elements exist.
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*/
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E nextElement();
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/**
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* Returns an {@link Iterator} that traverses the remaining elements
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* covered by this enumeration. Traversal is undefined if any methods
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* are called on this enumeration after the call to {@code asIterator}.
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*
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* @apiNote
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* This method is intended to help adapt code that produces
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* {@code Enumeration} instances to code that consumes {@code Iterator}
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* instances. For example, the {@link java.util.jar.JarFile#entries()
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* JarFile.entries()} method returns an {@code Enumeration<JarEntry>}.
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* This can be turned into an {@code Iterator}, and then the
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* {@code forEachRemaining()} method can be used:
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*
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* <pre>{@code
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* JarFile jarFile = ... ;
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* jarFile.entries().asIterator().forEachRemaining(entry -> { ... });
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* }</pre>
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*
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* (Note that there is also a {@link java.util.jar.JarFile#stream()
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* JarFile.stream()} method that returns a {@code Stream} of entries,
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* which may be more convenient in some cases.)
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*
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* @implSpec
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* The default implementation returns an {@code Iterator} whose
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* {@link Iterator#hasNext hasNext} method calls this Enumeration's
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* {@code hasMoreElements} method, whose {@link Iterator#next next}
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* method calls this Enumeration's {@code nextElement} method, and
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* whose {@link Iterator#remove remove} method throws
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* {@code UnsupportedOperationException}.
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*
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* @return an Iterator representing the remaining elements of this Enumeration
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*
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* @since 9
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*/
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default Iterator<E> asIterator() {
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return new Iterator<>() {
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@Override public boolean hasNext() {
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return hasMoreElements();
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}
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@Override public E next() {
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return nextElement();
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}
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};
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}
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}
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