almost.functional

Class Optional<T>

java.lang.Object

almost.functional.Optional<T>

public final class Optional<T>
extends java.lang.Object

A container object which may or may not contain a non-null value. If a value is present, isPresent() will return true and get() will return the value.

Method Summary

Methods

Modifier and Type	Method and Description
static <T> Optional<T>	empty() Returns an empty Optional instance.
Optional<T>	filter(Predicate<? super T> predicate) Apply a predicate to the optional, if the optional is present, and the predicate is true, return the optional, otherwise return empty.
T	get() If a value is present in this Optional, returns the value, otherwise throws NoSuchElementException.
Optional<T>	ifPresent(Consumer<? super T> consumer) If a value is present, invoke the specified consumer with the value, otherwise do nothing.
boolean	isPresent() Return true if there is a value present, otherwise false.
<V> Optional<V>	map(Function<T,V> function) If a value is present, map is with function, and if the result is non-null, return an Optional describing the result.
static <T> Optional<T>	of(T optionalValue) Returns an Optional with the specified present non-null value.
static <T> Optional<T>	ofNullable(T value) Returns an Optional of a value which might be null.
T	orElse(T other) Return the value if present, otherwise return other.
Optional<T>	orElseRun(java.lang.Runnable run) If the optional is empty run the Runnable.
T	orElseSupplier(Supplier<T> other) Return the value if present, otherwise get the value from the Supplier.
T	orElseThrow(java.lang.String msg) If optional is not empty return it's value, if empty throw a NoSuchElementException with message.

Methods inherited from class java.lang.Object

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

Method Detail

empty

public static <T> Optional<T> empty()

Returns an empty Optional instance. No value is present for this Optional.

Type Parameters:

T - Type of the non-existent value

Returns:

an empty Optional

of

public static <T> Optional<T> of(T optionalValue)

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

Type Parameters:

T - the class of the value

Parameters:

optionalValue - the value to be present, which must be non-null

Returns:

an Optional with the value present

ofNullable

public static <T> Optional<T> ofNullable(T value)

Returns an Optional of a value which might be null.

Type Parameters:

T - the type of the optional

Parameters:

value - the value

Returns:

an Optional of the value, or empty if value was null

filter

public Optional<T> filter(Predicate<? super T> predicate)

Apply a predicate to the optional, if the optional is present, and the predicate is true, return the optional, otherwise return empty.

Parameters:

predicate - the predicate to apply

Returns:

the optional if the predicate is true, empty if not

Since:

1.7

get

public T get()
      throws java.util.NoSuchElementException

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

Returns:

the non-null value held by this Optional

Throws:

java.util.NoSuchElementException

isPresent

public boolean isPresent()

Return true if there is a value present, otherwise false.

Returns:

true if there is a value present, otherwise false.

ifPresent

public Optional<T> ifPresent(Consumer<? super T> consumer)

If a value is present, invoke the specified consumer with the value, otherwise do nothing.

Parameters:

consumer - consumer to be invoked if present.

Returns:

this Optional

Since:

1.7.8

orElse

public 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

orElseRun

public Optional<T> orElseRun(java.lang.Runnable run)

If the optional is empty run the Runnable.

Parameters:

run - the runnable to run.

Returns:

This Optional

Since:

1.7.8

orElseSupplier

public T orElseSupplier(Supplier<T> other)

Return the value if present, otherwise get the value from the Supplier.

Parameters:

other - a Supplier

Returns:

the value, if present, or the return of the Supplier

Since:

1.7

orElseThrow

public T orElseThrow(java.lang.String msg)

If optional is not empty return it's value, if empty throw a NoSuchElementException with message.

Parameters:

msg - message for exception

Returns:

optional value if present

Throws:

java.util.NoSuchElementException - thrown if optional is empty

Since:

1.7.3

map

public <V> Optional<V> map(Function<T,V> function)

If a value is present, map is with function, and if the result is non-null, return an Optional describing the result. Otherwise return an empty Optional.

Type Parameters:

V - The type of the result of the mapping function

Parameters:

function - a map function to apply to the value, if present

Returns:

an Optional describing the result of map, if a value is present, otherwise an empty Optional