io.atlassian.fugue

Interface Maybe<A>

Type Parameters:

A - the contained type

All Superinterfaces:

Effect.Applicant<A>, Iterable<A>

All Known Subinterfaces:

Either.Projection<A,B,L,R>

All Known Implementing Classes:

Either.LeftProjection, Either.RightProjection, Option

public interface Maybe<A>
extends Iterable<A>, Effect.Applicant<A>

Implemented by things that may or may not contain a value.

Note there are some methods suggested by this interface that cannot be expressed here as the return type cannot be expressed in Java's type system (due to the lack of higher-kinded types). These are for instance (where M is the implementing Maybe sub-type):

• <B> Maybe<B> map(Function<? super A, B>)
• <B> Maybe<B> flatMap(Function<? super A, Maybe<B>>
• Maybe<A> filter(Predicate<? super A>)

Since:

1.0

Method Summary

Modifier and Type	Method and Description
boolean	exists(Predicate<? super A> p) Whether this is is defined and applying the predicate to the contained value returns true.
boolean	forall(Predicate<? super A> p) Returns true if empty or the result of the application of the given function to the value.
A	get() Get the value if defined.
A	getOr(Supplier<? extends A> supplier) Get the value if defined or call the supplier and return its value if not.
<B extends A> A	getOrElse(B other) Get the value if defined, otherwise returns other.
A	getOrElse(Supplier<? extends A> supplier) Deprecated. since 3.0 getOrElse(Supplier) is being replaced with getOr(Supplier). In Java 8 type inference cannot disambiguate between an overloaded method taking a generic A and the same method taking a Supplier<A>.
A	getOrError(Supplier<String> msg) Get the value or throws an error with the supplied message if not defined.
A	getOrNull() Get the value if defined or null if not.
<X extends Throwable> A	getOrThrow(Supplier<X> ifUndefined) Get the value or throws the supplied throwable if not defined.
boolean	isDefined() If the type contains a value return true.
boolean	isEmpty() If the type does not contain a value return true.
Iterator<A>	iterator() Return an iterator for this type.

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Methods inherited from interface io.atlassian.fugue.Effect.Applicant

foreach

Method Detail

get

A get()

Get the value if defined. Throw an exception otherwise.

Returns:

the wrapped value

Throws:

NoSuchElementException - if this is a none

getOrElse

<B extends A> A getOrElse(B other)

Get the value if defined, otherwise returns other.

Type Parameters:

B - default value type

Parameters:

other - value to return if this is empty

Returns:

wrapped value if this is defined, otherwise returns other

getOr

A getOr(Supplier<? extends A> supplier)

Get the value if defined or call the supplier and return its value if not. Replaces getOrElse(Supplier). Get the value if defined or call the supplier and return its value if not.

Parameters:

supplier - called if this is empty

Returns:

the wrapped value or the value from the Supplier

getOrElse

@Deprecated
A getOrElse(Supplier<? extends A> supplier)

Deprecated. since 3.0 getOrElse(Supplier) is being replaced with getOr(Supplier). In Java 8 type inference cannot disambiguate between an overloaded method taking a generic A and the same method taking a Supplier<A>.

Get the value if defined or call the supplier and return its value if not.

Parameters:

supplier - called if this is empty

Returns:

the wrapped value or the value from the Supplier

getOrNull

A getOrNull()

Get the value if defined or null if not.

Although the use of null is discouraged, code written to use these must often interface with code that expects and returns nulls.

Returns:

the value or null if not defined

getOrError

A getOrError(Supplier<String> msg)

Get the value or throws an error with the supplied message if not defined.

Used when absolutely sure this is defined.

Parameters:

msg - the message for the error.

Returns:

the contained value.

getOrThrow

<X extends Throwable> A getOrThrow(Supplier<X> ifUndefined)
                            throws X extends Throwable

Get the value or throws the supplied throwable if not defined.

Used when absolutely sure this is defined.

Type Parameters:

X - exception type

Parameters:

ifUndefined - the supplier of the throwable.

Returns:

the contained value.

Throws:

X - the throwable the supplier creates if there is no value.

X extends Throwable

Since:

2.0

isDefined

boolean isDefined()

If the type contains a value return true.

Returns:

true if this holds a value, false otherwise.

isEmpty

boolean isEmpty()

If the type does not contain a value return true.

Returns:

true if this does not hold a value, false otherwise.

exists

boolean exists(Predicate<? super A> p)

Whether this is is defined and applying the predicate to the contained value returns true.

Parameters:

p - the predicate to test, must not be null

Returns:

true if defined and the predicate returns true for the contained value, false otherwise.

iterator

Iterator<A> iterator()

Return an iterator for this type. In most cases this takes the form of an iterator returning zero or one values.

Specified by:

iterator in interface Iterable<A>

Returns:

an iterator over the contained value if defined, or an empty one otherwise.

forall

boolean forall(Predicate<? super A> p)

Returns true if empty or the result of the application of the given function to the value.

Parameters:

p - The predicate function to test on the contained value, must not be null

Returns:

true if no value or returns the result of the application of the given function to the value.