/*
* Copyright 2013 Stephen Connolly.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.jcip.annotations;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
/**
* The presence of this annotation indicates that the author believes the class
* to be immutable and hence inherently thread-safe. An immutable class is one
* where the state of an instance cannot be <i>seen</i> to change. As a result
* <ul>
* <li>All public fields must be {@code final}</li>
* <li>All public final reference fields are either {@code null} or refer to
* other immutable objects</li>
* <li>Constructors and methods do not publish references to any potentially
* mutable internal state.</li>
* </ul>
* Performance optimization may mean that instances of an immutable class may
* have mutable internal state. The critical point is that callers cannot tell
* the difference. For example {@link String} is an immutable class, despite
* having an internal int that is non-final but used as a cache for
* {@link String#hashCode()}.
* <p/>
* Immutable objects are inherently thread-safe; they may be passed between
* threads or published without synchronization.
*/
@Documented
@Target(TYPE)
@Retention(RUNTIME)
public @interface Immutable {
}