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/*
* Copyright (c) 2012, 2020, 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.
*
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package java8.util;
import java.util.NoSuchElementException;
import java8.util.function.IntConsumer;
import java8.util.function.IntSupplier;
import java8.util.function.Supplier;
import java8.util.stream.IntStream;
import java8.util.stream.IntStreams;
/**
* A container object which may or may not contain an {@code int} value.
* If a value is present, {@code isPresent()} returns {@code true}. If no
* value is present, the object is considered empty and
* {@code isPresent()} returns {@code false}.
*
* Additional methods that depend on the presence or absence of a contained
* value are provided, such as {@link #orElse(int) orElse()}
* (returns a default value if no value is present) and
* {@link #ifPresent(IntConsumer) ifPresent()} (performs an
* action if a 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 OptionalInt} may have unpredictable results and should be avoided.
*
*
API Note:
* {@code OptionalInt} is primarily intended for use as a method return type where
* there is a clear need to represent "no result". A variable whose type is
* {@code OptionalInt} should never itself be {@code null}; it should always point
* to an {@code OptionalInt} instance.
*
* @since 1.8
*/
public final class OptionalInt {
/**
* Common instance for {@code empty()}.
*/
private static final OptionalInt EMPTY = new OptionalInt();
/**
* If true then the value is present, otherwise indicates no value is present
*/
private final boolean isPresent;
private final int value;
private static final class OICache {
private OICache() {}
static final OptionalInt cache[] = new OptionalInt[-(-128) + 127 + 1];
static {
for (int i = 0; i < cache.length; i++) {
cache[i] = new OptionalInt(i - 128);
}
}
}
/**
* Construct an empty instance.
*
*
Implementation Note:
Generally only one empty instance, {@link OptionalInt#EMPTY},
* should exist per VM.
*/
private OptionalInt() {
this.isPresent = false;
this.value = 0;
}
/**
* Returns an empty {@code OptionalInt} instance. No value is present for
* this OptionalInt.
*
*
API Note:
* Though it may be tempting to do so, avoid testing if an object is empty
* by comparing with {@code ==} or {@code !=} against instances returned by
* {@code OptionalInt.empty()}. There is no guarantee that it is a singleton.
* Instead, use {@link #isEmpty()} or {@link #isPresent()}.
*
* @return an empty {@code OptionalInt}
*/
public static OptionalInt empty() {
return EMPTY;
}
/**
* Construct an instance with the described value.
*
* @param value the int value to describe
*/
OptionalInt(int value) {
this.isPresent = true;
this.value = value;
}
/**
* Returns an {@code OptionalInt} describing the given value.
*
* @param value the value to describe
* @return an {@code OptionalInt} with the value present
*/
public static OptionalInt of(int value) {
int offset = 128;
if (value >= -128 && value <= 127) { // will cache
return OICache.cache[value + offset];
}
return new OptionalInt(value);
}
/**
* If a value is present, returns the value, otherwise throws
* {@code NoSuchElementException}.
*
*
API Note:
* The preferred alternative to this method is {@link #orElseThrow()}.
*
* @return the value described by this {@code OptionalInt}
* @throws NoSuchElementException if no value is present
*/
public int getAsInt() {
return orElseThrow();
}
/**
* If a value is present, returns {@code true}, otherwise {@code false}.
*
* @return {@code true} if a value is present, otherwise {@code false}
*/
public boolean isPresent() {
return isPresent;
}
/**
* If a value is not present, returns {@code true}, otherwise
* {@code false}.
*
* @return {@code true} if a value is not present, otherwise {@code false}
* @since 11
*/
public boolean isEmpty() {
return !isPresent;
}
/**
* If a value is present, performs the given action with the value,
* otherwise does nothing.
*
* @param action the action to be performed, if a value is present
* @throws NullPointerException if a value is present and the given action is
* {@code null}
*/
public void ifPresent(IntConsumer action) {
if (isPresent) {
action.accept(value);
}
}
/**
* If a value is present, performs the given action with the value,
* otherwise performs the given empty-based action.
*
* @param action the action to be performed, if a value is present
* @param emptyAction the empty-based action to be performed, if no value is
* present
* @throws NullPointerException if a value is present and the given action
* is {@code null}, or no value is present and the given empty-based action
* is {@code null}.
* @since 9
*/
public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
if (isPresent) {
action.accept(value);
} else {
emptyAction.run();
}
}
/**
* If a value is present, returns a sequential {@link IntStream} containing
* only that value, otherwise returns an empty {@code IntStream}.
*
*
API Note:
* This method can be used to transform a {@code Stream} of optional
* integers to an {@code IntStream} of present integers:
*
*
{@code
* Stream os = ..
* IntStream s = os.flatMapToInt(OptionalInt::stream)
* }
*
* @return the optional value as an {@code IntStream}
* @since 9
*/
public IntStream stream() {
if (isPresent) {
return IntStreams.of(value);
} else {
return IntStreams.empty();
}
}
/**
* If a value is present, returns the value, otherwise returns
* {@code other}.
*
* @param other the value to be returned, if no value is present
* @return the value, if present, otherwise {@code other}
*/
public int orElse(int other) {
return isPresent ? value : other;
}
/**
* If a value is present, returns the value, otherwise returns the result
* produced by the supplying function.
*
* @param supplier the supplying function that produces a value to be returned
* @return the value, if present, otherwise the result produced by the
* supplying function
* @throws NullPointerException if no value is present and the supplying
* function is {@code null}
*/
public int orElseGet(IntSupplier supplier) {
return isPresent ? value : supplier.getAsInt();
}
/**
* If a value is present, returns the value, otherwise throws
* {@code NoSuchElementException}.
*
* @return the value described by this {@code OptionalInt}
* @throws NoSuchElementException if no value is present
* @since 10
*/
public int orElseThrow() {
if (!isPresent) {
throw new NoSuchElementException("No value present");
}
return value;
}
/**
* If a value is present, returns the value, otherwise throws an exception
* produced by the exception supplying function.
*
* API Note:
* A method reference to the exception constructor with an empty argument
* list can be used as the supplier. For example,
* {@code IllegalStateException::new}
*
* @param Type of the exception to be thrown
* @param exceptionSupplier the supplying function that produces an
* exception to be thrown
* @return the value, if present
* @throws X if no value is present
* @throws NullPointerException if no value is present and the exception
* supplying function is {@code null}
*/
public int orElseThrow(Supplier exceptionSupplier) throws X {
if (isPresent) {
return value;
} else {
throw exceptionSupplier.get();
}
}
/**
* Indicates whether some other object is "equal to" this
* {@code OptionalInt}. The other object is considered equal if:
*
* - it is also an {@code OptionalInt} and;
*
- both instances have no value present or;
*
- the present values are "equal to" each other via {@code ==}.
*
*
* @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 OptionalInt)) {
return false;
}
OptionalInt other = (OptionalInt) obj;
return (isPresent && other.isPresent)
? value == other.value
: isPresent == other.isPresent;
}
/**
* Returns the hash code of the value, if present, otherwise {@code 0}
* (zero) if no value is present.
*
* @return hash code value of the present value or {@code 0} if no value is
* present
*/
@Override
public int hashCode() {
return isPresent ? value : 0;
}
/**
* Returns a non-empty string representation of this {@code OptionalInt}
* suitable for debugging. The exact presentation format is unspecified and
* may vary between implementations and versions.
*
* Implementation Requirements:
* If a value is present the result must include its string representation
* in the result. Empty and present {@code OptionalInt}s must be
* unambiguously differentiable.
*
* @return the string representation of this instance
*/
@Override
public String toString() {
return isPresent
? String.format("OptionalInt[%s]", value)
: "OptionalInt.empty";
}
}