1 /*
2 * ====================================================================
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing,
14 * software distributed under the License is distributed on an
15 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16 * KIND, either express or implied. See the License for the
17 * specific language governing permissions and limitations
18 * under the License.
19 * ====================================================================
20 *
21 * This software consists of voluntary contributions made by many
22 * individuals on behalf of the Apache Software Foundation. For more
23 * information on the Apache Software Foundation, please see
24 * <http://www.apache.org/>.
25 *
26 */
27 package org.apache.http.annotation;
28
29 import java.lang.annotation.Documented;
30 import java.lang.annotation.ElementType;
31 import java.lang.annotation.Retention;
32 import java.lang.annotation.RetentionPolicy;
33 import java.lang.annotation.Target;
34
35 /**
36 * The class to which this annotation is applied is immutable. This means that
37 * its state cannot be seen to change by callers, which implies that
38 * <ul>
39 * <li> all public fields are final, </li>
40 * <li> all public final reference fields refer to other immutable objects, and </li>
41 * <li> constructors and methods do not publish references to any internal state
42 * which is potentially mutable by the implementation. </li>
43 * </ul>
44 * Immutable objects may still have internal mutable state for purposes of performance
45 * optimization; some state variables may be lazily computed, so long as they are computed
46 * from immutable state and that callers cannot tell the difference.
47 * <p>
48 * Immutable objects are inherently thread-safe; they may be passed between threads or
49 * published without synchronization.
50 * <p>
51 * Based on code developed by Brian Goetz and Tim Peierls and concepts
52 * published in 'Java Concurrency in Practice' by Brian Goetz, Tim Peierls,
53 * Joshua Bloch, Joseph Bowbeer, David Holmes and Doug Lea.
54 */
55 @Documented
56 @Target(ElementType.TYPE)
57 @Retention(RetentionPolicy.CLASS) // The original version used RUNTIME
58 public @interface Immutable {
59 }