xapi.inject.impl

Class SingletonProvider<X>

java.lang.Object

xapi.inject.impl.SingletonProvider<X>

Type Parameters:

X - - The type of data this var returns.

All Implemented Interfaces:

Provider<X>, ProvidesValue<X>

Direct Known Subclasses:

LazyHashMap, LazyLinkedList, LazyLinkedMap, LazyLinkedSet, LazyList, LazyProvider, LazySet, LazyTreeMap, SingletonInitializer

public abstract class SingletonProvider<X>
extends Object
implements Provider<X>, ProvidesValue<X>

A proxy class used to create a lazy-loading provider, with an efficient proxy (self-overwriting) proxy. .get() calls initialValue() on first load and replaces the initializer with a pojo getter. This allows for easy wrapping of lazily-loaded singletons without null-checking on every access.

Author:

James X Nelson (james@wetheinter.net, @ajax)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	SingletonProvider.NullCheckOnGet

Nested classes/interfaces inherited from interface xapi.util.api.ProvidesValue

ProvidesValue.NoOp<X>

Field Summary

Fields

Modifier and Type	Field and Description
protected Provider<X>	proxy The proxy object will override itself on first load with a bare pojo-based provider.

Constructor Summary

Constructors

Constructor and Description
SingletonProvider()

Method Summary

Modifier and Type	Method and Description
protected Provider<X>	createImmutableProvider(X init) Return a new proxy provider which just returns the set field.
X	get() This method is final so the compiler can optimize the call.
protected abstract X	initialValue() Called once, on first .get().
boolean	isSet() Tells whether or not this singleton is already set by instanceof checking the pojo class return from createImmutableProvider(Object).
protected void	onCreate(X init) Called whenever the object is initialized.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

proxy

protected Provider<X> proxy

The proxy object will override itself on first load with a bare pojo-based provider. In subclasses like @LazyPojo, this proxy object is toggled to allow for efficient get() when we can.

Constructor Detail

SingletonProvider

public SingletonProvider()

Method Detail

createImmutableProvider

protected Provider<X> createImmutableProvider(X init)

Return a new proxy provider which just returns the set field. NEVER return an instance of SingletonProvider.NullCheckOnGet, or you will contract a case of recursion sickness.

Parameters:

init - - A non-null value to provide immutably

Returns:

- An immutable provider. IF SUBCLASSES RETURN A PROVIDER THAT IS NOT A SUBCLASS OF ImmutableProvider, THEN YOU MUST OVERRIDE isSet() AS WELL.

isSet

public boolean isSet()

Tells whether or not this singleton is already set by instanceof checking the pojo class return from createImmutableProvider(Object). IF YOU OVERRIDE createImmutableProvider(Object), YOU MUST ALSO OVERRIDE isSet().

Returns:

- Whether or not our proxy class matches the expected immutable class.

onCreate

protected void onCreate(X init)

Called whenever the object is initialized. Will be called on the first successful get(), and every successful get() after a call to #reset()

Parameters:

init -

initialValue

protected abstract X initialValue()

Called once, on first .get(). Override to provide new value, or use @LazyPojo to set(X) externally.

Returns:

A singleton object that will be saved and returned on every subsequent .get()

get

public final X get()

This method is final so the compiler can optimize the call. This method is synchronized and null checks while the singleton is uninitialized, but once inited, it is unsynchronized with direct access, null-check free access to singleton.

Specified by:

get in interface Provider<X>

Specified by:

get in interface ProvidesValue<X>

Returns:

A value of type X whenever the owning object requests it.