Optional - JRE Emulation | JRE Emulation
public final class

Optional

extends Object
java.lang.Object
   ↳ java.util.Optional<T>

Class Overview

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
[Expand]
From class java.lang.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

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