no.digipost.concurrent

Class OneTimeAssignment<V>

java.lang.Object

no.digipost.concurrent.OneTimeAssignment<V>

Type Parameters:

V - The type of the object which is referenced.

All Implemented Interfaces:

ViewableAsOptional<V>

public final class OneTimeAssignment<V>
extends Object
implements ViewableAsOptional<V>

A reference which may or may not be assigned a value, with the added constraint that it can only be assigned once. If it is assigned a value more than one time it will throw an exception.

The class is thread-safe in the sense that it is not possible for concurrent threads to assign a value to it twice, though relevant cases for concurrent use are probably limited. The motivation is rather to enable fail-fast for erroneous API-usage involving assignments, e.g. builder implementations.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	OneTimeAssignment.AlreadyAssigned

Nested classes/interfaces inherited from interface no.digipost.util.ViewableAsOptional

ViewableAsOptional.TooManyElements

Method Summary

Modifier and Type	Method and Description
static <V> OneTimeAssignment<V>	defaultTo(Supplier<? extends V> defaultValue) Create a new non-assigned instance with a default value.
static <V> OneTimeAssignment<V>	defaultTo(V defaultValue) Create a new non-assigned instance with a default value.
V	get()
static <V> OneTimeAssignment<V>	newInstance() Create a new non-assigned instance.
void	set(V value) Assigns a value to this reference.
Optional<V>	toOptional() Convert this OneTimeAssignment to an Optional.

Methods inherited from class java.lang.Object

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

Method Detail

defaultTo

public static final <V> OneTimeAssignment<V> defaultTo(V defaultValue)

Create a new non-assigned instance with a default value.

Parameters:

defaultValue - The default value to use in case an assignment through set(Object) is never performed.

See Also:

defaultTo(Supplier)

defaultTo

public static final <V> OneTimeAssignment<V> defaultTo(Supplier<? extends V> defaultValue)

Create a new non-assigned instance with a default value.

Parameters:

defaultValue - The supplier to acquire the default value to use in case an assignment through set(Object) is never performed.

newInstance

public static final <V> OneTimeAssignment<V> newInstance()

Create a new non-assigned instance.

set

public void set(V value)

Assigns a value to this reference. This method can only be called once.

Parameters:

value - the value to set.

Throws:

OneTimeAssignment.AlreadyAssigned - if this reference is already assigned a value.

get

public V get()

Returns:

the referenced value. If the reference has not yet been set but is initialized with a default value, the reference is assigned the default value and this is returned.

toOptional

public Optional<V> toOptional()

Convert this OneTimeAssignment to an Optional. This method will never throw an exception. Calling this on an unassigned OneTimeAssignment with a default value, will effectively assign to the default value before wrapping it in an Optional.

Specified by:

toOptional in interface ViewableAsOptional<V>

Returns:

the Optional representation of this object.