1 /* 2 * Copyright (c) 2009, 2021, 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.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 */ 51 public 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 * @apiNote 58 * While this interface method is declared to throw {@code 59 * Exception}, implementers are <em>strongly</em> encouraged to 60 * declare concrete implementations of the {@code close} method to 61 * throw more specific exceptions, or to throw no exception at all 62 * if the close operation cannot fail. 63 * 64 * <p> Cases where the close operation may fail require careful 65 * attention by implementers. It is strongly advised to relinquish 66 * the underlying resources and to internally <em>mark</em> the 67 * resource as closed, prior to throwing the exception. The {@code 68 * close} method is unlikely to be invoked more than once and so 69 * this ensures that the resources are released in a timely manner. 70 * Furthermore it reduces problems that could arise when the resource 71 * wraps, or is wrapped, by another resource. 72 * 73 * <p><em>Implementers of this interface are also strongly advised 74 * to not have the {@code close} method throw {@link 75 * InterruptedException}.</em> 76 * 77 * This exception interacts with a thread's interrupted status, 78 * and runtime misbehavior is likely to occur if an {@code 79 * InterruptedException} is {@linkplain Throwable#addSuppressed 80 * suppressed}. 81 * 82 * More generally, if it would cause problems for an 83 * exception to be suppressed, the {@code AutoCloseable.close} 84 * method should not throw it. 85 * 86 * <p>Note that unlike the {@link java.io.Closeable#close close} 87 * method of {@link java.io.Closeable}, this {@code close} method 88 * is <em>not</em> required to be idempotent. In other words, 89 * calling this {@code close} method more than once may have some 90 * visible side effect, unlike {@code Closeable.close} which is 91 * required to have no effect if called more than once. 92 * 93 * However, implementers of this interface are strongly encouraged 94 * to make their {@code close} methods idempotent. 95 * 96 * @throws Exception if this resource cannot be closed 97 */ close()98 void close() throws Exception; 99 } 100