Package 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:

Consumer<V>, Supplier<V>, Assignment<V>, ViewableAsOptional<V>, ViewableAsOptional.Single<V>

public final class OneTimeAssignment<V>
extends Object
implements Assignment<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	Description
static final class	OneTimeAssignment.AlreadyAssigned

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

ViewableAsOptional.Single<V>, ViewableAsOptional.TooManyElements

Method Summary

Modifier and Type	Method	Description
static final <V> OneTimeAssignment<V>	defaultTo(Supplier<? extends V> defaultValue)	Create a new non-assigned instance with a default value.
static final <V> OneTimeAssignment<V>	defaultTo(V defaultValue)	Create a new non-assigned instance with a default value.
V	get()
boolean	isSet()	Determine if this OneTimeAssignment has been set, either by using set(Object) or implicitly by a default value, triggered with a call to get().
static final <V> OneTimeAssignment<V>	newInstance()	Create a new non-assigned instance.
void	set(V value)	Assigns a value to this reference.

Methods inherited from class java.lang.Object

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

Methods inherited from interface no.digipost.util.Assignment

accept, chainableWith

Methods inherited from interface java.util.function.Consumer

andThen

Methods inherited from interface no.digipost.util.ViewableAsOptional.Single

toOptional

Method Details

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.

Specified by:

set in interface Assignment<V>

Parameters:

value - the value to set.

Throws:

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

isSet

public boolean isSet()

Determine if this OneTimeAssignment has been set, either by using set(Object) or implicitly by a default value, triggered with a call to get().

For sake of clarity, an invocation of this method does never implicitly assign any default value. An assignment with no default value requires an invocation of set(Object) for this method to return true.

Returns:

true if the assignment has a value, false if it has not been assigned yet.

get

public V get()

Specified by:

get in interface Supplier<V>

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.