Optional

AI-generated Key Takeaways

• Optional is a container object that may or may not hold a non-null value, helping to avoid NullPointerExceptions.

• It provides methods like isPresent() to check for value presence and get() to retrieve the value if present.

• orElse() and ifPresent() offer ways to handle value presence or absence gracefully.

• Optional can be created using methods such as empty(), of(), and ofNullable().

• Methods like map(), flatMap(), and filter() allow for functional-style operations on the contained value.

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).

Public Method Summary

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 Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Methods

public static Optional<T> empty ()

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

Returns

• an empty Optional

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;
• both instances have no value present or;
• the present values are "equal to" each other via equals().

Parameters

obj	an object to be tested for equality

Returns

• {code true} if the other object is "equal to" this object otherwise false

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	a predicate to apply to the value, if present

Returns

• 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

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(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	a mapping function to apply to the value, if present the mapping function

Returns

• 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

public T get ()

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

Returns

• the non-null value held by this Optional

Throws

NoSuchElementException	if there is no value present

See Also

• isPresent()

public int hashCode ()

Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.

Returns

• hash code value of the present value or 0 if no value is present

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

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

Parameters

consumer	block to be executed if a value is present

Throws

NullPointerException	if value is present and consumer is null

public boolean isPresent ()

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

Returns

• true if there is a value present, otherwise false

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.

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 Optional, if a value is present, otherwise an empty Optional

Throws

NullPointerException	if the mapping function is null

public static Optional<T> of (T value)

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

Parameters

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

Returns

• an Optional with the value present

Throws

NullPointerException	if value is null

public static Optional<T> ofNullable (T value)

Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.

Parameters

value	the possibly-null value to describe

Returns

• an Optional with a present value if the specified value is non-null, otherwise an empty Optional

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

public T orElseGet (Supplier<? extends T> other)

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

Parameters

other	a Supplier whose result is returned if no value is present

Returns

• the value if present otherwise the result of other.get()

Throws

NullPointerException	if value is not present and other is null

public T orElseThrow (Supplier<? extends X> exceptionSupplier)

Return the contained value, if present, otherwise throw an exception to be created by the provided supplier.

Parameters

exceptionSupplier	The supplier which will return the exception to be thrown

Returns

• the present value

Throws

	if there is no value present
NullPointerException	if no value is present and exceptionSupplier is null
Throwable

public String toString ()

Returns a non-empty string representation of this Optional suitable for debugging. The exact presentation format is unspecified and may vary between implementations and versions.

Returns

• the string representation of this instance