1 /*
2 * Copyright (c) 1994, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 /**
29 * An object that implements the Enumeration interface generates a
30 * series of elements, one at a time. Successive calls to the
31 * {@code nextElement} method return successive elements of the
32 * series.
33 * <p>
34 * For example, to print all elements of a {@code Vector<E>} <i>v</i>:
35 * <pre>
36 * for (Enumeration<E> e = v.elements(); e.hasMoreElements();)
37 * System.out.println(e.nextElement());</pre>
38 * <p>
39 * Methods are provided to enumerate through the elements of a
40 * vector, the keys of a hashtable, and the values in a hashtable.
41 * Enumerations are also used to specify the input streams to a
42 * {@code SequenceInputStream}.
43 *
44 * @apiNote
45 * The functionality of this interface is duplicated by the {@link Iterator}
46 * interface. In addition, {@code Iterator} adds an optional remove operation,
47 * and has shorter method names. New implementations should consider using
48 * {@code Iterator} in preference to {@code Enumeration}. It is possible to
49 * adapt an {@code Enumeration} to an {@code Iterator} by using the
50 * {@link #asIterator} method.
51 *
52 * @see java.util.Iterator
53 * @see java.io.SequenceInputStream
54 * @see java.util.Enumeration#nextElement()
55 * @see java.util.Hashtable
56 * @see java.util.Hashtable#elements()
57 * @see java.util.Hashtable#keys()
58 * @see java.util.Vector
59 * @see java.util.Vector#elements()
60 *
61 * @author Lee Boynton
62 * @since 1.0
63 */
64 public interface Enumeration<E> {
65 /**
66 * Tests if this enumeration contains more elements.
67 *
68 * @return {@code true} if and only if this enumeration object
69 * contains at least one more element to provide;
70 * {@code false} otherwise.
71 */
72 boolean hasMoreElements();
73
74 /**
75 * Returns the next element of this enumeration if this enumeration
76 * object has at least one more element to provide.
77 *
78 * @return the next element of this enumeration.
79 * @exception NoSuchElementException if no more elements exist.
80 */
81 E nextElement();
82
83 /**
84 * Returns an {@link Iterator} that traverses the remaining elements
85 * covered by this enumeration. Traversal is undefined if any methods
86 * are called on this enumeration after the call to {@code asIterator}.
87 *
88 * @apiNote
89 * This method is intended to help adapt code that produces
90 * {@code Enumeration} instances to code that consumes {@code Iterator}
91 * instances. For example, the {@link java.util.jar.JarFile#entries
92 * JarFile.entries()} method returns an {@code Enumeration<JarEntry>}.
93 * This can be turned into an {@code Iterator}, and then the
94 * {@code forEachRemaining()} method can be used:
95 *
96 * <pre>{@code
97 * JarFile jarFile = ... ;
98 * jarFile.entries().asIterator().forEachRemaining(entry -> { ... });
99 * }</pre>
100 *
101 * (Note that there is also a {@link java.util.jar.JarFile#stream
102 * JarFile.stream()} method that returns a {@code Stream} of entries,
103 * which may be more convenient in some cases.)
104 *
105 * @implSpec
106 * The default implementation returns an {@code Iterator} whose
107 * {@link Iterator#hasNext hasNext} method calls this Enumeration's
108 * {@code hasMoreElements} method, whose {@link Iterator#next next}
109 * method calls this Enumeration's {@code nextElement} method, and
110 * whose {@link Iterator#remove remove} method throws
111 * {@code UnsupportedOperationException}.
112 *
113 * @return an Iterator representing the remaining elements of this Enumeration
114 *
115 * @since 9
116 */
117 default Iterator<E> asIterator() {
118 return new Iterator<>() {
119 @Override public boolean hasNext() {
120 return hasMoreElements();
121 }
122 @Override public E next() {
123 return nextElement();
124 }
125 };
126 }
127 }