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</code> method return successive elements of the
32 * series.
33 * <p>
34 * For example, to print all elements of a <tt>Vector<E></tt> <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</code>.
43 * <p>
44 * NOTE: The functionality of this interface is duplicated by the Iterator
45 * interface. In addition, Iterator adds an optional remove operation, and
46 * has shorter method names. New implementations should consider using
47 * Iterator in preference to Enumeration.
48 *
49 * @see java.util.Iterator
50 * @see java.io.SequenceInputStream
51 * @see java.util.Enumeration#nextElement()
52 * @see java.util.Hashtable
53 * @see java.util.Hashtable#elements()
54 * @see java.util.Hashtable#keys()
55 * @see java.util.Vector
56 * @see java.util.Vector#elements()
57 *
58 * @author Lee Boynton
59 * @since 1.0
60 */
61 public interface Enumeration<E> {
62 /**
63 * Tests if this enumeration contains more elements.
64 *
65 * @return <code>true</code> if and only if this enumeration object
66 * contains at least one more element to provide;
67 * <code>false</code> otherwise.
68 */
69 boolean hasMoreElements();
70
71 /**
72 * Returns the next element of this enumeration if this enumeration
73 * object has at least one more element to provide.
74 *
75 * @return the next element of this enumeration.
76 * @exception NoSuchElementException if no more elements exist.
77 */
78 E nextElement();
79
80 /**
81 * Returns an {@link Iterator} whose elements are the same as the
82 * elements of this {@code Enumeration}. The results are undefined
83 * if this method is called more than once, or if this Enumeration's
84 * other methods are called after {@code asIterator} has been called.
85 *
86 * @apiNote
87 * This method is intended to help adapt code that produces
88 * {@code Enumeration} instances to code that consumes {@code Iterator}
89 * or {@code Iterable} instances. For example, the
90 * {@link java.security.PermissionCollection PermissionCollection.elements()}
91 * method returns an {@code Enumeration<Permission>}. This can be adapted
92 * for use in an enhanced-for loop as follows:
93 *
94 * <pre>{@code
95 * PermissionCollection pc = ... ;
96 * Iterable<Permission> permsIterable = () -> pc.elements().asIterator();
97 * for (Permission p : permsIterable) {
98 * doSomethingWithPermission(p);
99 * }
100 * }</pre>
101 *
102 * A {@code Stream<Permission>} could be created from an
103 * {@code Enumeration<Permission>} as follows:
104 *
105 * <pre>{@code
106 * Stream<Permission> permsStream = StreamSupport.stream(
107 * Spliterators.spliteratorUnknownSize(
108 * pc.elements().asIterator(),
109 * Spliterator.ORDERED | Spliterator.IMMUTABLE),
110 * false);
111 * }</pre>
112 *
113 * @implSpec
114 * The returned Iterator's {@link Iterator#hasNext hasNext} method calls and returns
115 * the value from this Enumeration's {@code hasMoreElements} method; its
116 * {@link Iterator#next next} method calls and returns the value from this Enumeration's
117 * {@code nextElement} method; and its {@link Iterator#remove remove} method throws
118 * {@code UnsupportedOperationException}.
119 *
120 * @return an Iterator derived from this Enumeration
121 *
122 * @since 1.9
123 */
124 default Iterator<E> asIterator() {
125 return new Iterator<E>() {
126 @Override public boolean hasNext() {
127 return Enumeration.this.hasMoreElements();
128 }
129 @Override public E next() {
130 return Enumeration.this.nextElement();
131 }
132 };
133 }
134 }