org.osgl

Class Lang.Option<T>

java.lang.Object

org.osgl.Lang.Option<T>

Type Parameters:

T - the element type

All Implemented Interfaces:

Serializable, Iterable<T>

Direct Known Subclasses:

Lang.None, Lang.Some

Enclosing class:

Lang

public abstract static class Lang.Option<T>
extends Object
implements Iterable<T>, Serializable

Defines an option of element T. This class can be used to implement the else-if semantic in functional programming and eliminate the null value

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	Lang.Option.f The runtime/instance function namespace

Field Summary

Fields

Modifier and Type	Field and Description
Lang.Option.f	f A reference to this runtime function namesapce

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object obj)
Lang.Option<T>	filter(Lang.Function<? super T,Boolean> predicate) If a value is present, and the value matches the given predicate, return an Option describing the value, otherwise return Lang.NONE.
<B> Lang.Option<B>	flatMap(Lang.Function<? super T,Lang.Option<B>> mapper) If a value is present, apply the provided Option-bearing mapping function to it, return that result, otherwise return Lang.NONE.
abstract T	get() If a value is present in this Option, returns the value, otherwise throws NoSuchElementException.
int	hashCode()
boolean	isDefined() Returns true if this Option is not Lang.NONE
<B> Lang.Option<B>	map(Lang.Function<? super T,? extends B> mapper) If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Option describing the result.
static <T> Lang.None<T>	none()
boolean	notDefined() Negate of isDefined()
static <T> Lang.Option<T>	of(T value) Returns an Option with the specified present value if it is not null or Lang.NONE otherwise.
T	orElse(Lang.Func0<? extends T> other) Return the value if present, otherwise invoke other and return the result of that invocation.
T	orElse(T other) Return the value if present, otherwise return other.
void	runWith(Lang.Visitor<? super T> consumer)
static <T> Lang.Some<T>	some(T value) Returns an Option with the specified present non-null value.
abstract String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, iterator, spliterator

Field Detail

f

public final Lang.Option.f f

A reference to this runtime function namesapce

Method Detail

isDefined

public final boolean isDefined()

Returns true if this Option is not Lang.NONE

Returns:

true if there is a value present, otherwise false

Since:

0.2

notDefined

public boolean notDefined()

Negate of isDefined()

Returns:

true if this option is not defined

Since:

0.2

get

public abstract T get()
               throws NoSuchElementException

If a value is present in this Option, returns the value, otherwise throws NoSuchElementException.

Returns:

the non-null value held by this Option

Throws:

NoSuchElementException - if this Option is Lang.NONE

filter

public final Lang.Option<T> filter(Lang.Function<? super T,Boolean> predicate)

If a value is present, and the value matches the given predicate, return an Option describing the value, otherwise return Lang.NONE.

Parameters:

predicate - the function to test the value held by this Option

Returns:

an Option describing the value of this Option if a value is present and the value matches the given predicate, otherwise Lang.NONE

map

public final <B> Lang.Option<B> map(Lang.Function<? super T,? extends B> mapper)

If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Option describing the result. Otherwise return Lang.NONE.

Type Parameters:

B - The type of the result of the mapping function

Parameters:

mapper - a mapping function to apply to the value, if present

Returns:

an Optional describing the result of applying a mapping function to the value of this Option, if a value is present, otherwise Lang.NONE

Throws:

NullPointerException - if the mapper function is null

Since:

0.2

flatMap

public final <B> Lang.Option<B> flatMap(Lang.Function<? super T,Lang.Option<B>> mapper)

If a value is present, apply the provided Option-bearing mapping function to it, return that result, otherwise return Lang.NONE. This method is similar to #map(Function), but the provided mapper is one whose result is already an Option, and if invoked, flatMap does not wrap it with an additional Option.

Type Parameters:

B - The type parameter to the Option returned by

Parameters:

mapper - a mapping function to apply to the value,

Returns:

the result of applying an Option-bearing mapping function to the value of this Option, if a value is present, otherwise Lang.NONE

Throws:

NullPointerException - if the mapping function is null or returns a null result

Since:

0.2

orElse

public final T orElse(T other)

Return the value if present, otherwise return other.

Parameters:

other - the value to be returned if there is no value present, may be null

Returns:

the value, if present, otherwise other

orElse

public final T orElse(Lang.Func0<? extends T> other)

Return the value if present, otherwise invoke other and return the result of that invocation.

Parameters:

other - the function that is applied when no value is presented

Returns:

the value if present otherwise the result of other.apply()

Throws:

NullPointerException - if value is not present and other is null

Since:

0.2

runWith

public final void runWith(Lang.Visitor<? super T> consumer)

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public abstract String toString()

Overrides:

toString in class Object

none

public static <T> Lang.None<T> none()

some

public static <T> Lang.Some<T> some(T value)

Returns an Option with the specified present non-null value.

Type Parameters:

T - the type of the value

Parameters:

value - the value that cannot be null

Returns:

an Option instance describing the value

Throws:

NullPointerException - if the value specified is null

Since:

0.2

of

public static <T> Lang.Option<T> of(T value)

Returns an Option with the specified present value if it is not null or Lang.NONE otherwise.

Type Parameters:

T - the type of the value

Parameters:

value - the value

Returns:

an Option describing the value if it is not null or Lang.NONE if the value is null

Since:

0.2