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*
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
*
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package java.util;
import java.util.function.DoubleConsumer;
import java.util.function.DoubleSupplier;
import java.util.function.Supplier;
import java.util.stream.DoubleStream;
/**
* A container object which may or may not contain a {@code double} value. If a
* value is present, {@code isPresent()} returns {@code true} and
* {@code getAsDouble()} returns the value.
*
* <p>Additional methods that depend on the presence or absence of a contained
* value are provided, such as {@link #orElse(double) orElse()}
* (returns a default value if no value is present) and
* {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()} (performs
* an action if a 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 OptionalDouble} may have unpredictable results and should be avoided.
*
* @since 1.8
*/
public final class OptionalDouble {
/**
* Common instance for {@code empty()}.
*/
private static final OptionalDouble EMPTY = new OptionalDouble();
/**
* If true then the value is present, otherwise indicates no value is present
*/
private final boolean isPresent;
private final double value;
/**
* Construct an empty instance.
*
* @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
* should exist per VM.
*/
private OptionalDouble() {
this.isPresent = false;
this.value = Double.NaN;
}
/**
* Returns an empty {@code OptionalDouble} instance. No value is present
* for this {@code OptionalDouble}.
*
* @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 OptionalDouble.empty()}. There is no guarantee that it is a singleton.
* Instead, use {@link #isPresent()}.
*
* @return an empty {@code OptionalDouble}.
*/
public static OptionalDouble empty() {
return EMPTY;
}
/**
* Construct an instance with the described value.
*
* @param value the double value to describe.
*/
private OptionalDouble(double value) {
this.isPresent = true;
this.value = value;
}
/**
* Returns an {@code OptionalDouble} describing the given value.
*
* @param value the value to describe
* @return an {@code OptionalDouble} with the value present
*/
public static OptionalDouble of(double value) {
return new OptionalDouble(value);
}
/**
* If a value is present, returns the value, otherwise throws
* {@code NoSuchElementException}.
*
* @return the value described by this {@code OptionalDouble}
* @throws NoSuchElementException if no value is present
* @see OptionalDouble#isPresent()
*/
public double getAsDouble() {
if (!isPresent) {
throw new NoSuchElementException("No value present");
}
return value;
}
/**
* 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 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 value is present and the given action is
* {@code null}
*/
public void ifPresent(DoubleConsumer 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(DoubleConsumer action, Runnable emptyAction) {
if (isPresent) {
action.accept(value);
} else {
emptyAction.run();
}
}
/**
* If a value is present, returns a sequential {@link DoubleStream}
* containing only that value, otherwise returns an empty
* {@code DoubleStream}.
*
* @apiNote
* This method can be used to transform a {@code Stream} of optional doubles
* to a {@code DoubleStream} of present doubles:
* <pre>{@code
* Stream<OptionalDouble> os = ..
* DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
* }</pre>
*
* @return the optional value as a {@code DoubleStream}
* @since 9
*/
public DoubleStream stream() {
if (isPresent) {
return DoubleStream.of(value);
} else {
return DoubleStream.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 double orElse(double 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 double orElseGet(DoubleSupplier supplier) {
return isPresent ? value : supplier.getAsDouble();
}
/**
* If a value is present, returns the value, otherwise throws an exception
* produced by the exception supplying function.
*
* @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 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<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
if (isPresent) {
return value;
} else {
throw exceptionSupplier.get();
}
}
/**
* Indicates whether some other object is "equal to" this
* {@code OptionalDouble}. The other object is considered equal if:
* <ul>
* <li>it is also an {@code OptionalDouble} and;
* <li>both instances have no value present or;
* <li>the present values are "equal to" each other via
* {@code Double.compare() == 0}.
* </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 OptionalDouble)) {
return false;
}
OptionalDouble other = (OptionalDouble) obj;
return (isPresent && other.isPresent)
? Double.compare(value, other.value) == 0
: 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 ? Double.hashCode(value) : 0;
}
/**
* Returns a non-empty string representation of this {@code OptionalDouble}
* 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 {@code OptionalDouble}s must be
* unambiguously differentiable.
*
* @return the string representation of this instance
*/
@Override
public String toString() {
return isPresent
? String.format("OptionalDouble[%s]", value)
: "OptionalDouble.empty";
}
}