groovy.lang.Singleton Maven / Gradle / Ivy
/*
* Copyright 2008 the original author or authors.
*
* 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 groovy.lang;
import org.codehaus.groovy.transform.GroovyASTTransformationClass;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Class annotation to make class singleton.
*
* Singleton can be initialized in static initialization of the class or lazily (on first access)
* To make singleton lazy it is enough to use {@code @Singleton(lazy=true)}
* Lazy singletons implemented with double check locking and volatile field
*
* @author Alex Tkachman
*/
@java.lang.annotation.Documented
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.TYPE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.SingletonASTTransformation")
public @interface Singleton {
/**
* @return if this singleton should be lazy
*/
boolean lazy () default false;
/**
* @return the singleton property name
*/
String property() default "instance";
}