com.landawn.abacus.util

Class Nullable<T>

java.lang.Object

com.landawn.abacus.util.Any<T>

com.landawn.abacus.util.Nullable<T>

public final class Nullable<T>
extends Any<T>

Note: It's copied from OpenJDK at: http://hg.openjdk.java.net/jdk8u/hs-dev/jdk
A container object which may or may not contain a nullable 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).

This is a value-based class; use of identity-sensitive operations (including reference equality (==), identity hash code, or synchronization) on instances of Nullable may have unpredictable results and should be avoided.

Method Summary

Modifier and Type	Method and Description
static <T> Nullable<T>	empty() Returns an empty Nullable instance.
boolean	equals(java.lang.Object obj) Indicates whether some other object is "equal to" this Optional.
<E extends java.lang.Exception> Nullable<T>	filter(Try.Predicate<? super T,E> predicate) If a value is present, and the value matches the given predicate, return an Nullable describing the value, otherwise return an empty Nullable.
<E extends java.lang.Exception> Nullable<T>	filterIfNotNull(Try.Predicate<? super T,E> predicate) If a value is not null, and the value matches the given predicate, return an Nullable describing the value, otherwise return an empty Nullable.
<U,E extends java.lang.Exception> Nullable<U>	flatMap(Try.Function<? super T,? extends Any<U>,E> mapper) If a value is present, apply the provided Nullable-bearing mapping function to it, return that result, otherwise return an empty Nullable.
<U,E extends java.lang.Exception> Nullable<U>	flatMapIfNotNull(Try.Function<? super T,? extends Any<U>,E> mapper) If a value is not null, apply the provided Nullable-bearing mapping function to it, return that result, otherwise return an empty Nullable.
int	hashCode() Returns the hash code value of the present value, if any, or 0 (zero) if no value is present.
<U,E extends java.lang.Exception> Nullable<U>	map(Try.Function<? super T,? extends U,E> mapper) If a value is present, apply the provided mapping function to it,
<U,E extends java.lang.Exception> Nullable<U>	mapIfNotNull(Try.Function<? super T,? extends U,E> mapper) If a value is not null, apply the provided mapping function to it,
static <T> Nullable<T>	of(T value) Returns an Nullable with the specified present nullable value.
<E extends java.lang.Exception> Nullable<T>	or(Try.Supplier<? extends Any<T>,E> supplier) Returns this if it's present or call supplier.get().
java.lang.String	toString() Returns a non-empty string representation of this Optional suitable for debugging.

Methods inherited from class com.landawn.abacus.util.Any

get, ifNotNull, ifNotNullOrElse, ifPresent, ifPresentOrElse, isNotNull, isPresent, orElse, orElseGet, orElseThrow, orGetIfNull, orIfNull, orThrowIfNull, stream, streamIfNotNull, toJdkOptional, toList, toListIfNotNull, toOptional, toSet, toSetIfNotNull

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Method Detail

empty

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

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

Type Parameters:

T - Type of the non-existent value

Returns:

an empty Nullable

of

public static <T> Nullable<T> of(T value)

Returns an Nullable with the specified present nullable value.

Parameters:

value - the value to be present, which could be null

Returns:

an Nullable with the value present

filter

public <E extends java.lang.Exception> Nullable<T> filter(Try.Predicate<? super T,E> predicate)
                                                   throws E extends java.lang.Exception

If a value is present, and the value matches the given predicate, return an Nullable describing the value, otherwise return an empty Nullable.

Specified by:

filter in class Any<T>

Parameters:

predicate - a predicate to apply to the value, if present

Returns:

an Nullable describing the value of this Nullable if a value is present and the value matches the given predicate, otherwise an empty Nullable

Throws:

java.lang.NullPointerException - if the predicate is null

E extends java.lang.Exception

map

public <U,E extends java.lang.Exception> Nullable<U> map(Try.Function<? super T,? extends U,E> mapper)
                                                  throws E extends java.lang.Exception

If a value is present, apply the provided mapping function to it,

Specified by:

map in class Any<T>

Type Parameters:

U - The type of the result of the mapping function

Parameters:

mapper - a mapping function to apply to the value, if present

Returns:

an Nullable describing the result of applying a mapping function to the value of this Nullable, if a value is present, otherwise an empty Nullable

Throws:

java.lang.NullPointerException - if the mapping function is null

E extends java.lang.Exception

flatMap

public <U,E extends java.lang.Exception> Nullable<U> flatMap(Try.Function<? super T,? extends Any<U>,E> mapper)
                                                      throws E extends java.lang.Exception

If a value is present, apply the provided Nullable-bearing mapping function to it, return that result, otherwise return an empty Nullable. This method is similar to #map(Function), but the provided mapper is one whose result is already an Nullable, and if invoked, flatMap does not wrap it with an additional Nullable.

Specified by:

flatMap in class Any<T>

Type Parameters:

U - The type parameter to the Nullable returned by

Parameters:

mapper - a mapping function to apply to the value, if present the mapping function

Returns:

the result of applying an Nullable-bearing mapping function to the value of this Nullable, if a value is present, otherwise an empty Nullable

Throws:

java.lang.NullPointerException - if the mapping function is null or returns a null result

E extends java.lang.Exception

filterIfNotNull

public <E extends java.lang.Exception> Nullable<T> filterIfNotNull(Try.Predicate<? super T,E> predicate)
                                                            throws E extends java.lang.Exception

If a value is not null, and the value matches the given predicate, return an Nullable describing the value, otherwise return an empty Nullable.

Specified by:

filterIfNotNull in class Any<T>

Parameters:

predicate - a predicate to apply to the value, if present

Returns:

an Nullable describing the value of this Nullable if a value is present and the value matches the given predicate, otherwise an empty Nullable

Throws:

java.lang.NullPointerException - if the predicate is null

E extends java.lang.Exception

mapIfNotNull

public <U,E extends java.lang.Exception> Nullable<U> mapIfNotNull(Try.Function<? super T,? extends U,E> mapper)
                                                           throws E extends java.lang.Exception

If a value is not null, apply the provided mapping function to it,

Specified by:

mapIfNotNull in class Any<T>

Type Parameters:

U - The type of the result of the mapping function

Parameters:

mapper - a mapping function to apply to the value, if not null

Returns:

an Nullable describing the result of applying a mapping function to the value of this Nullable, if a value is not null, otherwise an empty Nullable

Throws:

java.lang.NullPointerException - if the mapping function is null

E extends java.lang.Exception

flatMapIfNotNull

public <U,E extends java.lang.Exception> Nullable<U> flatMapIfNotNull(Try.Function<? super T,? extends Any<U>,E> mapper)
                                                               throws E extends java.lang.Exception

If a value is not null, apply the provided Nullable-bearing mapping function to it, return that result, otherwise return an empty Nullable. This method is similar to #map(Function), but the provided mapper is one whose result is already an Nullable, and if invoked, flatMap does not wrap it with an additional Nullable.

Specified by:

flatMapIfNotNull in class Any<T>

Type Parameters:

U - The type parameter to the Nullable returned by

Parameters:

mapper - a mapping function to apply to the value, if not null the mapping function

Returns:

the result of applying an Nullable-bearing mapping function to the value of this Nullable, if a value is not null, otherwise an empty Nullable

Throws:

java.lang.NullPointerException - if the mapping function is null or returns a null result

E extends java.lang.Exception

or

public <E extends java.lang.Exception> Nullable<T> or(Try.Supplier<? extends Any<T>,E> supplier)
                                               throws E extends java.lang.Exception

Returns this if it's present or call supplier.get().

Specified by:

or in class Any<T>

Parameters:

supplier -

Returns:

Throws:

E

E extends java.lang.Exception

equals

public boolean equals(java.lang.Object obj)

Indicates whether some other object is "equal to" this Optional. The other object is considered equal if:

• it is also an Nullable and;
• both instances have no value present or;
• the present values are "equal to" each other via equals().

Overrides:

equals in class java.lang.Object

Parameters:

obj - an object to be tested for equality

Returns:

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

hashCode

public int hashCode()

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

Overrides:

hashCode in class java.lang.Object

Returns:

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

toString

public java.lang.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.

Overrides:

toString in class java.lang.Object

Returns:

the string representation of this instance