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OptionalLong.java
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/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;
import java.util.function.LongConsumer;
import java.util.function.LongSupplier;
import java.util.function.Supplier;
/**
* A container object which may or may not contain a {@code long} value.
* If a value is present, {@code isPresent()} will return {@code true} and
* {@code getAsLong()} will return the value.
*
* <p>Additional methods that depend on the presence or absence of a contained
* value are provided, such as {@link #orElse(long) orElse()}
* (return a default value if value not present) and
* {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (execute a block
* of code if the value is present).
*
* <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
* class; use of identity-sensitive operations (including reference equality
* ({@code ==}), identity hash code, or synchronization) on instances of
* {@code OptionalLong} may have unpredictable results and should be avoided.
*
* @since 1.8
*/
public final class OptionalLong {
/**
* Common instance for {@code empty()}.
*/
private static final OptionalLong EMPTY = new OptionalLong();
/**
* If true then the value is present, otherwise indicates no value is present
*/
private final boolean isPresent;
private final long value;
/**
* Construct an empty instance.
*
* @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
* should exist per VM.
*/
private OptionalLong() {
this.isPresent = false;
this.value = 0;
}
/**
* Returns an empty {@code OptionalLong} instance. No value is present for this
* OptionalLong.
*
* @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 Option.empty()}. There is no guarantee that it is a singleton.
* Instead, use {@link #isPresent()}.
*
* @return an empty {@code OptionalLong}.
*/
public static OptionalLong empty() {
return EMPTY;
}
/**
* Construct an instance with the value present.
*
* @param value the long value to be present
*/
private OptionalLong(long value) {
this.isPresent = true;
this.value = value;
}
/**
* Return an {@code OptionalLong} with the specified value present.
*
* @param value the value to be present
* @return an {@code OptionalLong} with the value present
*/
public static OptionalLong of(long value) {
return new OptionalLong(value);
}
/**
* If a value is present in this {@code OptionalLong}, returns the value,
* otherwise throws {@code NoSuchElementException}.
*
* @return the value held by this {@code OptionalLong}
* @throws NoSuchElementException if there is no value present
*
* @see OptionalLong#isPresent()
*/
public long getAsLong() {
if (!isPresent) {
throw new NoSuchElementException("No value present");
}
return value;
}
/**
* Return {@code true} if there is a value present, otherwise {@code false}.
*
* @return {@code true} if there is a value present, otherwise {@code false}
*/
public boolean isPresent() {
return isPresent;
}
/**
* Have the specified consumer accept the value if a value is present,
* otherwise do nothing.
*
* @param consumer block to be executed if a value is present
* @throws NullPointerException if value is present and {@code consumer} is
* null
*/
public void ifPresent(LongConsumer consumer) {
if (isPresent)
consumer.accept(value);
}
/**
* Return the value if present, otherwise return {@code other}.
*
* @param other the value to be returned if there is no value present
* @return the value, if present, otherwise {@code other}
*/
public long orElse(long other) {
return isPresent ? value : other;
}
/**
* Return the value if present, otherwise invoke {@code other} and return
* the result of that invocation.
*
* @param other a {@code LongSupplier} whose result is returned if no value
* is present
* @return the value if present otherwise the result of {@code other.getAsLong()}
* @throws NullPointerException if value is not present and {@code other} is
* null
*/
public long orElseGet(LongSupplier other) {
return isPresent ? value : other.getAsLong();
}
/**
* Return the contained value, if present, otherwise throw an exception
* to be created by the provided supplier.
*
* @apiNote A method reference to the exception constructor with an empty
* argument list can be used as the supplier. For example,
* {@code IllegalStateException::new}
*
* @param <X> Type of the exception to be thrown
* @param exceptionSupplier The supplier which will return the exception to
* be thrown
* @return the present value
* @throws X if there is no value present
* @throws NullPointerException if no value is present and
* {@code exceptionSupplier} is null
*/
public<X extends Throwable> long orElseThrow(Supplier<X> exceptionSupplier) throws X {
if (isPresent) {
return value;
} else {
throw exceptionSupplier.get();
}
}
/**
* Indicates whether some other object is "equal to" this OptionalLong. The
* other object is considered equal if:
* <ul>
* <li>it is also an {@code OptionalLong} and;
* <li>both instances have no value present or;
* <li>the present values are "equal to" each other via {@code ==}.
* </ul>
*
* @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 OptionalLong)) {
return false;
}
OptionalLong other = (OptionalLong) obj;
return (isPresent && other.isPresent)
? value == other.value
: isPresent == other.isPresent;
}
/**
* 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 isPresent ? Long.hashCode(value) : 0;
}
/**
* {@inheritDoc}
*
* Returns a non-empty string representation of this object 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 instances must be
* unambiguously differentiable.
*
* @return the string representation of this instance
*/
@Override
public String toString() {
return isPresent
? String.format("OptionalLong[%s]", value)
: "OptionalLong.empty";
}
}