1/*
2 * Copyright (c) 2009, 2013, 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
26package java.lang;
27
28/**
29 * An object that may hold resources (such as file or socket handles)
30 * until it is closed. The {@link #close()} method of an {@code AutoCloseable}
31 * object is called automatically when exiting a {@code
32 * try}-with-resources block for which the object has been declared in
33 * the resource specification header. This construction ensures prompt
34 * release, avoiding resource exhaustion exceptions and errors that
35 * may otherwise occur.
36 *
37 * @apiNote
38 * <p>It is possible, and in fact common, for a base class to
39 * implement AutoCloseable even though not all of its subclasses or
40 * instances will hold releasable resources.  For code that must operate
41 * in complete generality, or when it is known that the {@code AutoCloseable}
42 * instance requires resource release, it is recommended to use {@code
43 * try}-with-resources constructions. However, when using facilities such as
44 * {@link java.util.stream.Stream} that support both I/O-based and
45 * non-I/O-based forms, {@code try}-with-resources blocks are in
46 * general unnecessary when using non-I/O-based forms.
47 *
48 * @author Josh Bloch
49 * @since 1.7
50 */
51public interface AutoCloseable {
52    /**
53     * Closes this resource, relinquishing any underlying resources.
54     * This method is invoked automatically on objects managed by the
55     * {@code try}-with-resources statement.
56     *
57     * <p>While this interface method is declared to throw {@code
58     * Exception}, implementers are <em>strongly</em> encouraged to
59     * declare concrete implementations of the {@code close} method to
60     * throw more specific exceptions, or to throw no exception at all
61     * if the close operation cannot fail.
62     *
63     * <p> Cases where the close operation may fail require careful
64     * attention by implementers. It is strongly advised to relinquish
65     * the underlying resources and to internally <em>mark</em> the
66     * resource as closed, prior to throwing the exception. The {@code
67     * close} method is unlikely to be invoked more than once and so
68     * this ensures that the resources are released in a timely manner.
69     * Furthermore it reduces problems that could arise when the resource
70     * wraps, or is wrapped, by another resource.
71     *
72     * <p><em>Implementers of this interface are also strongly advised
73     * to not have the {@code close} method throw {@link
74     * InterruptedException}.</em>
75     *
76     * This exception interacts with a thread's interrupted status,
77     * and runtime misbehavior is likely to occur if an {@code
78     * InterruptedException} is {@linkplain Throwable#addSuppressed
79     * suppressed}.
80     *
81     * More generally, if it would cause problems for an
82     * exception to be suppressed, the {@code AutoCloseable.close}
83     * method should not throw it.
84     *
85     * <p>Note that unlike the {@link java.io.Closeable#close close}
86     * method of {@link java.io.Closeable}, this {@code close} method
87     * is <em>not</em> required to be idempotent.  In other words,
88     * calling this {@code close} method more than once may have some
89     * visible side effect, unlike {@code Closeable.close} which is
90     * required to have no effect if called more than once.
91     *
92     * However, implementers of this interface are strongly encouraged
93     * to make their {@code close} methods idempotent.
94     *
95     * @throws Exception if this resource cannot be closed
96     */
97    void close() throws Exception;
98}
99