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/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package com.landawn.abacus.util;
/**
* 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, {@code isPresent()} will return {@code true} and
* {@code get()} will return the value.
*
* Additional methods that depend on the presence or absence of a contained
* value are provided, such as {@link #or(java.lang.Object) orElse()}
* (return a default value if value not present) and
* {@link #ifPresent(java.util.function.Consumers) 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
* ({@code ==}), identity hash code, or synchronization) on instances of
* {@code Nullable} may have unpredictable results and should be avoided.
*
*/
public final class Nullable extends Any {
/**
* Common instance for {@code empty()}.
*/
private static final Nullable EMPTY = new Nullable<>();
/**
* Constructs an empty instance.
*
* @implNote Generally only one empty instance, {@link Nullable#EMPTY},
* should exist per VM.
*/
private Nullable() {
super();
}
/**
* Constructs an instance with the value present.
*
* @param value the nullable value to be present
*/
private Nullable(T value) {
super(value);
}
/**
* Returns an empty {@code Nullable} instance. No value is present for this
* Optional.
*
* @apiNote Though it may be tempting to do so, avoid testing if an object
* is empty by comparing with {@code ==} against instances returned by
* {@code Nullable.empty()}. There is no guarantee that it is a singleton.
* Instead, use {@link #isPresent()}.
*
* @param Type of the non-existent value
* @return an empty {@code Nullable}
*/
public static Nullable empty() {
return (Nullable) EMPTY;
}
/**
* Returns an {@code Nullable} with the specified present nullable value.
*
* @param value the value to be present, which could be null
* @return an {@code Nullable} with the value present
*/
public static Nullable of(T value) {
return new Nullable<>(value);
}
public static Nullable from(Optional optional) {
return optional.isPresent() ? of(optional.get()) : Nullable. empty();
}
public static Nullable from(java.util.Optional optional) {
return optional.isPresent() ? of(optional.get()) : Nullable. empty();
}
/**
* If a value is present, and the value matches the given predicate,
* return an {@code Nullable} describing the value, otherwise return an
* empty {@code Nullable}.
*
* @param predicate a predicate to apply to the value, if present
* @return an {@code Nullable} describing the value of this {@code Nullable}
* if a value is present and the value matches the given predicate,
* otherwise an empty {@code Nullable}
* @throws IllegalArgumentException if the predicate is null
*/
@Override
public Nullable filter(Try.Predicate predicate) throws E {
N.checkArgNotNull(predicate);
if (isPresent() && predicate.test(value)) {
return this;
} else {
return empty();
}
}
/**
* If a value is present, apply the provided mapping function to it,
*
* @apiNote 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
* {@code Optional}:
*
* {@code
* Nullable fis =
* names.stream().filter(name -> !isProcessedYet(name))
* .findFirst()
* .map(name -> new FileInputStream(name));
* }
*
* Here, {@code findFirst} returns an {@code Nullable}, and then
* {@code map} returns an {@code Nullable} for the desired
* file if one exists.
*
* @param The type of the result of the mapping function
* @param mapper a mapping function to apply to the value, if present
* @return an {@code Nullable} describing the result of applying a mapping
* function to the value of this {@code Nullable}, if a value is present,
* otherwise an empty {@code Nullable}
* @throws IllegalArgumentException if the mapping function is null
*/
@Override
public Nullable map(Try.Function mapper) throws E {
N.checkArgNotNull(mapper);
if (isPresent()) {
return Nullable.of((U) mapper.apply(value));
} else {
return empty();
}
}
/**
* If a value is present, apply the provided {@code Nullable}-bearing
* mapping function to it, return that result, otherwise return an empty
* {@code Nullable}. This method is similar to {@link #map(Function)},
* but the provided mapper is one whose result is already an {@code Nullable},
* and if invoked, {@code flatMap} does not wrap it with an additional
* {@code Nullable}.
*
* @param The type parameter to the {@code Nullable} returned by
* @param mapper a mapping function to apply to the value, if present
* the mapping function
* @return the result of applying an {@code Nullable}-bearing mapping
* function to the value of this {@code Nullable}, if a value is present,
* otherwise an empty {@code Nullable}
* @throws IllegalArgumentException if the mapping function is null or returns
* a null result
*/
@Override
public Nullable flatMap(Try.Function, E> mapper) throws E {
N.checkArgNotNull(mapper);
if (isPresent()) {
final Any any = N.checkArgNotNull(mapper.apply(value));
return any instanceof Nullable ? (Nullable) any : (any.isPresent ? Nullable.of(any.get()) : Nullable. empty());
} else {
return empty();
}
}
/**
* If a value is not null, and the value matches the given predicate,
* return an {@code Optional} describing the value, otherwise return an
* empty {@code Optional}.
*
* @param predicate a predicate to apply to the value, if present
* @return an {@code Optional} describing the value of this {@code Optional}
* if a value is present and the value matches the given predicate,
* otherwise an empty {@code Optional}
* @throws IllegalArgumentException if the predicate is null
*/
@Override
public Optional filterIfNotNull(Try.Predicate predicate) throws E {
N.checkArgNotNull(predicate);
if (isNotNull() && predicate.test(value)) {
return Optional.of(value);
} else {
return Optional.empty();
}
}
/**
* If a value is not null, apply the provided mapping function to it,
*
* @apiNote 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
* {@code Optional}:
*
* {@code
* Nullable fis =
* names.stream().filter(name -> !isProcessedYet(name))
* .findFirst()
* .map(name -> new FileInputStream(name));
* }
*
* Here, {@code findFirst} returns an {@code Nullable}, and then
* {@code map} returns an {@code Optional} for the desired
* file if one exists.
*
* @param The type of the result of the mapping function
* @param mapper a mapping function to apply to the value, if not null
* @return an {@code Nullable} describing the result of applying a mapping
* function to the value of this {@code Nullable}, if a value is not null,
* otherwise an empty {@code Nullable}
* @throws IllegalArgumentException if the mapping function is null
*/
@Override
public Nullable mapIfNotNull(Try.Function mapper) throws E {
N.checkArgNotNull(mapper);
if (isNotNull()) {
return Nullable.of((U) mapper.apply(value));
} else {
return empty();
}
}
/**
* If a value is not null, apply the provided {@code Nullable}-bearing
* mapping function to it, return that result, otherwise return an empty
* {@code Nullable}. This method is similar to {@link #map(Function)},
* but the provided mapper is one whose result is already an {@code Nullable},
* and if invoked, {@code flatMap} does not wrap it with an additional
* {@code Nullable}.
*
* @param The type parameter to the {@code Nullable} returned by
* @param mapper a mapping function to apply to the value, if not null
* the mapping function
* @return the result of applying an {@code Nullable}-bearing mapping
* function to the value of this {@code Nullable}, if a value is not null,
* otherwise an empty {@code Nullable}
* @throws IllegalArgumentException if the mapping function is null or returns
* a null result
*/
@Override
public Nullable flatMapIfNotNull(Try.Function, E> mapper) throws E {
N.checkArgNotNull(mapper);
if (isNotNull()) {
final Any any = N.checkArgNotNull(mapper.apply(value));
return any instanceof Nullable ? (Nullable) any : (any.isPresent ? Nullable.of(any.get()) : Nullable. empty());
} else {
return empty();
}
}
/**
* Returns {@code this} if it's present or call {@code supplier.get()}.
*
* @param supplier
* @return
* @throws E
*/
@Override
public Nullable or(Try.Supplier, E> supplier) throws E {
if (isPresent()) {
return this;
} else {
final Any any = N.checkArgNotNull(supplier.get());
return any instanceof Nullable ? (Nullable) any : (any.isPresent ? Nullable.of(any.get()) : Nullable. empty());
}
}
/**
* Indicates whether some other object is "equal to" this Optional. The other object is considered equal if:
*
* - it is also an {@code Nullable} and;
*
- both instances have no value present or;
*
- the present values are "equal to" each other via {@code equals()}.
*
*
* @param obj an object to be tested for equality
* @return {code true} if the other object is "equal to" this object
* otherwise {@code false}
*/
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj instanceof Nullable) {
final Nullable other = (Nullable) obj;
return N.equals(isPresent, other.isPresent) && N.equals(value, other.value);
}
return false;
}
/**
* Returns the hash code value of the present value, if any, or 0 (zero) if
* no value is present.
*
* @return hash code value of the present value or 0 if no value is present
*/
@Override
public int hashCode() {
return N.hashCode(isPresent) * 31 + N.hashCode(value);
}
/**
* 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.
*
* @implSpec If a value is present the result must include its string
* representation in the result. Empty and present Optionals must be
* unambiguously differentiable.
*
* @return the string representation of this instance
*/
@Override
public String toString() {
return isPresent ? String.format("Nullable[%s]", value) : "Nullable.empty";
}
}