de.team33.patterns.lazy.narvi

Class Lazy<T>

java.lang.Object

de.team33.patterns.lazy.narvi.Lazy<T>

public class Lazy<T>
extends Object

Implements a kind of supplier that provides a virtually fixed value. That value is only actually determined when it is accessed for the first time.

This implementation ensures that the originally defined initialization code is called at most once, even if there is concurrent access from multiple threads, unless the initialization attempt causes a RuntimeException.

Once the value is established, unnecessary effort to synchronize competing* read accesses is avoided.

*Pure read accesses are of course not really competing.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Lazy.InitException An unchecked exception type that may be thrown, when the initialization code of a Lazy instance causes a checked exception.

Method Summary

Modifier and Type	Method and Description
T	get() Executes the originally defined initialization code once on the first call and returns its result on that and every subsequent call without executing the initialization code again.
static <T> Lazy<T>	init(Supplier<? extends T> initial) Returns a new Lazy instance giving a Supplier that defines the intended initialization of the represented value.
static <T> Lazy<T>	initEx(XSupplier<? extends T,?> initial) Returns a new Lazy instance giving an XSupplier that defines the intended initialization of the represented value.

Methods inherited from class java.lang.Object

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

Method Detail

init

public static <T> Lazy<T> init(Supplier<? extends T> initial)

Returns a new Lazy instance giving a Supplier that defines the intended initialization of the represented value.

Type Parameters:

T - The result type of the initialisation code.

See Also:

initEx(XSupplier)

initEx

public static <T> Lazy<T> initEx(XSupplier<? extends T,?> initial)

Returns a new Lazy instance giving an XSupplier that defines the intended initialization of the represented value. The initialization code may throw a checked exception. If so, it is caught, wrapped in an Lazy.InitException, and rethrown.

Type Parameters:

T - The result type of the initialisation code.

See Also:

init(Supplier)

get

public final T get()

Executes the originally defined initialization code once on the first call and returns its result on that and every subsequent call without executing the initialization code again. This method is thread safe.