author | smarks |
Thu, 20 Apr 2017 11:40:57 -0700 | |
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parent 33238 | 80720cbea36f |
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/* |
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* Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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package java.util; |
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|
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import java.util.function.DoubleConsumer; |
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import java.util.function.DoubleSupplier; |
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import java.util.function.Supplier; |
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import java.util.stream.DoubleStream; |
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/** |
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* A container object which may or may not contain a {@code double} value. If a |
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* value is present, {@code isPresent()} returns {@code true} and |
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* {@code getAsDouble()} returns the value. |
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* |
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* <p>Additional methods that depend on the presence or absence of a contained |
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* value are provided, such as {@link #orElse(double) orElse()} |
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* (returns a default value if no value is present) and |
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* {@link #ifPresent(DoubleConsumer) ifPresent()} (performs |
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* an action if a value is present). |
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* |
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* <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a> |
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* class; use of identity-sensitive operations (including reference equality |
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* ({@code ==}), identity hash code, or synchronization) on instances of |
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* {@code OptionalDouble} may have unpredictable results and should be avoided. |
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* |
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* @apiNote |
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* {@code OptionalDouble} is primarily intended for use as a method return type where |
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* there is a clear need to represent "no result." A variable whose type is |
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* {@code OptionalDouble} should never itself be {@code null}; it should always point |
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* to an {@code OptionalDouble} instance. |
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* |
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* @since 1.8 |
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*/ |
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public final class OptionalDouble { |
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/** |
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* Common instance for {@code empty()}. |
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*/ |
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private static final OptionalDouble EMPTY = new OptionalDouble(); |
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/** |
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* If true then the value is present, otherwise indicates no value is present |
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*/ |
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private final boolean isPresent; |
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private final double value; |
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/** |
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* Construct an empty instance. |
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* |
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* @implNote generally only one empty instance, {@link OptionalDouble#EMPTY}, |
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* should exist per VM. |
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*/ |
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private OptionalDouble() { |
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this.isPresent = false; |
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this.value = Double.NaN; |
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} |
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/** |
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* Returns an empty {@code OptionalDouble} instance. No value is present |
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* for this {@code OptionalDouble}. |
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* |
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* @apiNote |
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* Though it may be tempting to do so, avoid testing if an object is empty |
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* by comparing with {@code ==} against instances returned by |
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* {@code OptionalDouble.empty()}. There is no guarantee that it is a singleton. |
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* Instead, use {@link #isPresent()}. |
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* |
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* @return an empty {@code OptionalDouble}. |
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*/ |
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public static OptionalDouble empty() { |
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return EMPTY; |
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} |
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/** |
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* Construct an instance with the described value. |
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* |
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* @param value the double value to describe. |
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*/ |
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private OptionalDouble(double value) { |
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this.isPresent = true; |
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this.value = value; |
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} |
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/** |
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* Returns an {@code OptionalDouble} describing the given value. |
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* |
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* @param value the value to describe |
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* @return an {@code OptionalDouble} with the value present |
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*/ |
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public static OptionalDouble of(double value) { |
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return new OptionalDouble(value); |
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} |
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/** |
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* If a value is present, returns the value, otherwise throws |
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* {@code NoSuchElementException}. |
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* |
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* @apiNote |
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* The methods {@link #orElse(double) orElse} and |
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* {@link #orElseGet(DoubleSupplier) orElseGet} |
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* are generally preferable to this method, as they return a substitute |
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* value if the value is absent, instead of throwing an exception. |
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* |
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* @return the value described by this {@code OptionalDouble} |
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* @throws NoSuchElementException if no value is present |
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* @see OptionalDouble#isPresent() |
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*/ |
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public double getAsDouble() { |
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if (!isPresent) { |
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throw new NoSuchElementException("No value present"); |
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} |
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return value; |
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} |
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/** |
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* If a value is present, returns {@code true}, otherwise {@code false}. |
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* |
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* @return {@code true} if a value is present, otherwise {@code false} |
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*/ |
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public boolean isPresent() { |
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return isPresent; |
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} |
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/** |
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* If a value is present, performs the given action with the value, |
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* otherwise does nothing. |
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* |
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* @param action the action to be performed, if a value is present |
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* @throws NullPointerException if value is present and the given action is |
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* {@code null} |
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*/ |
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public void ifPresent(DoubleConsumer action) { |
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if (isPresent) { |
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action.accept(value); |
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} |
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} |
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/** |
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* If a value is present, performs the given action with the value, |
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* otherwise performs the given empty-based action. |
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* |
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* @param action the action to be performed, if a value is present |
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* @param emptyAction the empty-based action to be performed, if no value is |
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* present |
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* @throws NullPointerException if a value is present and the given action |
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* is {@code null}, or no value is present and the given empty-based |
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* action is {@code null}. |
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* @since 9 |
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*/ |
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public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) { |
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if (isPresent) { |
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action.accept(value); |
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} else { |
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emptyAction.run(); |
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} |
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} |
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/** |
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* If a value is present, returns a sequential {@link DoubleStream} |
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* containing only that value, otherwise returns an empty |
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* {@code DoubleStream}. |
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* |
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* @apiNote |
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* This method can be used to transform a {@code Stream} of optional doubles |
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* to a {@code DoubleStream} of present doubles: |
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* <pre>{@code |
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* Stream<OptionalDouble> os = .. |
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* DoubleStream s = os.flatMapToDouble(OptionalDouble::stream) |
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* }</pre> |
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* |
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* @return the optional value as a {@code DoubleStream} |
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* @since 9 |
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*/ |
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public DoubleStream stream() { |
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if (isPresent) { |
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return DoubleStream.of(value); |
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} else { |
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return DoubleStream.empty(); |
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} |
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} |
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/** |
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* If a value is present, returns the value, otherwise returns |
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* {@code other}. |
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* |
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* @param other the value to be returned, if no value is present |
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* @return the value, if present, otherwise {@code other} |
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*/ |
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public double orElse(double other) { |
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return isPresent ? value : other; |
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} |
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/** |
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* If a value is present, returns the value, otherwise returns the result |
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* produced by the supplying function. |
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* |
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* @param supplier the supplying function that produces a value to be returned |
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* @return the value, if present, otherwise the result produced by the |
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* supplying function |
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* @throws NullPointerException if no value is present and the supplying |
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* function is {@code null} |
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*/ |
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public double orElseGet(DoubleSupplier supplier) { |
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return isPresent ? value : supplier.getAsDouble(); |
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} |
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|
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/** |
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* If a value is present, returns the value, otherwise throws an exception |
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* produced by the exception supplying function. |
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* |
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* @apiNote |
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* A method reference to the exception constructor with an empty argument |
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* list can be used as the supplier. For example, |
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* {@code IllegalStateException::new} |
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* |
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* @param <X> Type of the exception to be thrown |
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* @param exceptionSupplier the supplying function that produces an |
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* exception to be thrown |
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* @return the value, if present |
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* @throws X if no value is present |
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* @throws NullPointerException if no value is present and the exception |
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* supplying function is {@code null} |
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*/ |
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public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { |
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if (isPresent) { |
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return value; |
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} else { |
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throw exceptionSupplier.get(); |
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} |
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} |
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|
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/** |
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* Indicates whether some other object is "equal to" this |
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* {@code OptionalDouble}. The other object is considered equal if: |
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* <ul> |
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* <li>it is also an {@code OptionalDouble} and; |
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* <li>both instances have no value present or; |
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* <li>the present values are "equal to" each other via |
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* {@code Double.compare() == 0}. |
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* </ul> |
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* |
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* @param obj an object to be tested for equality |
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* @return {@code true} if the other object is "equal to" this object |
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* otherwise {@code false} |
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*/ |
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@Override |
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public boolean equals(Object obj) { |
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if (this == obj) { |
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return true; |
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} |
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|
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if (!(obj instanceof OptionalDouble)) { |
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return false; |
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} |
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|
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OptionalDouble other = (OptionalDouble) obj; |
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return (isPresent && other.isPresent) |
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? Double.compare(value, other.value) == 0 |
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: isPresent == other.isPresent; |
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} |
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/** |
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* Returns the hash code of the value, if present, otherwise {@code 0} |
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* (zero) if no value is present. |
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* |
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* @return hash code value of the present value or {@code 0} if no value is |
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* present |
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*/ |
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@Override |
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public int hashCode() { |
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return isPresent ? Double.hashCode(value) : 0; |
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} |
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|
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/** |
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* Returns a non-empty string representation of this {@code OptionalDouble} |
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* suitable for debugging. The exact presentation format is unspecified and |
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* may vary between implementations and versions. |
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* |
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* @implSpec |
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* If a value is present the result must include its string representation |
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* in the result. Empty and present {@code OptionalDouble}s must be |
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* unambiguously differentiable. |
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* |
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* @return the string representation of this instance |
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*/ |
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@Override |
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public String toString() { |
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return isPresent |
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? String.format("OptionalDouble[%s]", value) |
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: "OptionalDouble.empty"; |
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} |
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} |