groovy.lang
[Java] Annotation Type Singleton

java.lang.Object
  groovy.lang.Singleton

@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.TYPE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.SingletonASTTransformation")
public @interface Singleton

Class annotation to make a singleton class. The singleton is obtained through normal property access using the singleton property (defaults to "instance"). Such classes can be initialized during normal static initialization of the class or lazily (on first access). To make the singleton lazy use @Singleton(lazy=true). Lazy singletons are implemented with double-checked locking and a volatile backing field. By default, no explicit constructors are allowed. To create one or more explicit constructors use @Singleton(strict=false). This could be used to:

• provide your own custom initialization logic in your own no-arg constructor - you will be responsible for the entire code (the @Singleton annotation becomes merely documentation)
• provide one or more constructors with arguments for a quasi-singleton - these constructors will be used to create instances that are independent of the singleton instance returned by the singleton property

Authors:

Alex Tkachman

Paul King

lazy

public boolean lazy

@default false

Returns:

if this singleton should be lazy

property

public String property

@default "instance"

Returns:

the singleton property name

strict

public boolean strict

@default true

Returns:

if this singleton should have strict semantics

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