Optional

public final class Optional

extends 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.

Additional methods that depend on the presence or absence of a contained value are provided, such as orElse() (return a default value if value not present) and ifPresent() (execute a block of code if the value is present).

Summary

Public methods static <T> Optional<T> empty() Returns an empty Optional instance. boolean equals(Object obj) Indicates whether some other object is "equal to" this Optional. Optional<T> filter(Predicate<? super T> predicate) If a value is present, and the value matches the given predicate, return an Optional describing the value, otherwise return an empty Optional . <U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) If a value is present, apply the provided Optional -bearing mapping function to it, return that result, otherwise return an empty Optional . T get() If a value is present in this Optional , returns the value, otherwise throws NoSuchElementException . int hashCode() Returns the hash code value of the present value, if any, or 0 (zero) if no value is present. void 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 . <U> Optional<U> map(Function<? super T, ? extends U> mapper) If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result. static <T> Optional<T> of(T value) Returns an Optional with the specified present non-null value. static <T> Optional<T> ofNullable(T value) Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional . T orElse(T other) Return the value if present, otherwise return other . T orElseGet(Supplier<? extends T> other) Return the value if present, otherwise invoke other and return the result of that invocation. <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) Return the contained value, if present, otherwise throw an exception to be created by the provided supplier. String toString() Returns a non-empty string representation of this Optional suitable for debugging.

Inherited methods java.lang.Object From class Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object . int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeout, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long timeout) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Public methods

empty Added in API level 24 public static Optional<T> empty () Returns an empty Optional instance. No value is present for this Optional. API Note: Though it may be tempting to do so, avoid testing if an object is empty by comparing with == against instances returned by Option.empty() . There is no guarantee that it is a singleton. Instead, use isPresent() . Returns Optional<T> an empty Optional

equals Added in API level 24 public boolean equals (Object obj) Indicates whether some other object is "equal to" this Optional. The other object is considered equal if: it is also an Optional and;

and; both instances have no value present or;

the present values are "equal to" each other via equals() . Parameters obj Object : an object to be tested for equality Returns boolean {code true} if the other object is "equal to" this object otherwise false

filter Added in API level 24 public Optional<T> filter (Predicate<? super T> predicate) If a value is present, and the value matches the given predicate, return an Optional describing the value, otherwise return an empty Optional . Parameters predicate Predicate : a predicate to apply to the value, if present Returns Optional<T> an Optional describing the value of this Optional if a value is present and the value matches the given predicate, otherwise an empty Optional Throws NullPointerException if the predicate is null

flatMap Added in API level 24 public Optional<U> flatMap (Function<? super T, Optional<U>> mapper) If a value is present, apply the provided Optional -bearing mapping function to it, return that result, otherwise return an empty Optional . This method is similar to map(java.util.function.Function) , but the provided mapper is one whose result is already an Optional , and if invoked, flatMap does not wrap it with an additional Optional . Parameters mapper Function : a mapping function to apply to the value, if present the mapping function Returns Optional<U> the result of applying an Optional -bearing mapping function to the value of this Optional , if a value is present, otherwise an empty Optional Throws NullPointerException if the mapping function is null or returns a null result

get Added in API level 24 public T get () If a value is present in this Optional , returns the value, otherwise throws NoSuchElementException . Returns T the non-null value held by this Optional Throws NoSuchElementException if there is no value present See also: isPresent()

hashCode Added in API level 24 public int hashCode () Returns the hash code value of the present value, if any, or 0 (zero) if no value is present. Returns int hash code value of the present value or 0 if no value is present

ifPresent Added in API level 24 public void ifPresent (Consumer<? super T> consumer) If a value is present, invoke the specified consumer with the value, otherwise do nothing. Parameters consumer Consumer : block to be executed if a value is present Throws NullPointerException if value is present and consumer is null

isPresent Added in API level 24 public boolean isPresent () Return true if there is a value present, otherwise false . Returns boolean true if there is a value present, otherwise false

map Added in API level 24 public Optional<U> map (Function<? super T, ? extends U> mapper) If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result. Otherwise return an empty Optional . API Note: This method supports post-processing on optional values, without the need to explicitly check for a return status. For example, the following code traverses a stream of file names, selects one that has not yet been processed, and then opens that file, returning an Optional<FileInputStream> : Optional<FileInputStream> fis = names.stream().filter(name -> !isProcessedYet(name)) .findFirst() .map(name -> new FileInputStream(name)); Here, findFirst returns an Optional<String> , and then map returns an Optional<FileInputStream> for the desired file if one exists. Parameters mapper Function : a mapping function to apply to the value, if present Returns Optional<U> an Optional describing the result of applying a mapping function to the value of this Optional , if a value is present, otherwise an empty Optional Throws NullPointerException if the mapping function is null

of Added in API level 24 public static Optional<T> of (T value) Returns an Optional with the specified present non-null value. Parameters value T : the value to be present, which must be non-null Returns Optional<T> an Optional with the value present Throws NullPointerException if value is null

ofNullable Added in API level 24 public static Optional<T> ofNullable (T value) Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional . Parameters value T : the possibly-null value to describe Returns Optional<T> an Optional with a present value if the specified value is non-null, otherwise an empty Optional

orElse Added in API level 24 public T orElse (T other) Return the value if present, otherwise return other . Parameters other T : the value to be returned if there is no value present, may be null Returns T the value, if present, otherwise other

orElseGet Added in API level 24 public T orElseGet (Supplier<? extends T> other) Return the value if present, otherwise invoke other and return the result of that invocation. Parameters other Supplier : a Supplier whose result is returned if no value is present Returns T the value if present otherwise the result of other.get() Throws NullPointerException if value is not present and other is null

orElseThrow Added in API level 24 public T orElseThrow (Supplier<? extends X> exceptionSupplier) Return the contained value, if present, otherwise throw an exception to be created by the provided supplier. API Note: A method reference to the exception constructor with an empty argument list can be used as the supplier. For example, IllegalStateException::new Parameters exceptionSupplier Supplier : The supplier which will return the exception to be thrown Returns T the present value Throws if there is no value present NullPointerException if no value is present and exceptionSupplier is null Throwable