--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/OptionalLong.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,311 @@
+/*
+ * Copyright (c) 2012, 2017, 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package java.util;
+
+import java.util.function.LongConsumer;
+import java.util.function.LongSupplier;
+import java.util.function.Supplier;
+import java.util.stream.LongStream;
+
+/**
+ * A container object which may or may not contain a {@code long} value. If a
+ * value is present, {@code isPresent()} returns {@code true} and
+ * {@code getAsLong()} returns the value.
+ *
+ * <p>Additional methods that depend on the presence or absence of a contained
+ * value are provided, such as {@link #orElse(long) orElse()}
+ * (returns a default value if no value is present) and
+ * {@link #ifPresent(LongConsumer) 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 OptionalLong} may have unpredictable results and should be avoided.
+ *
+ * @apiNote
+ * {@code OptionalLong} 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 OptionalLong} should never itself be {@code null}; it should always point
+ * to an {@code OptionalLong} instance.
+ *
+ * @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 {@code 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 OptionalLong.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 described value.
+ *
+ * @param value the long value to describe
+ */
+ private OptionalLong(long value) {
+ this.isPresent = true;
+ this.value = value;
+ }
+
+ /**
+ * Returns an {@code OptionalLong} describing the given value.
+ *
+ * @param value the value to describe
+ * @return an {@code OptionalLong} with the value present
+ */
+ public static OptionalLong of(long value) {
+ return new OptionalLong(value);
+ }
+
+ /**
+ * If a value is present, returns the value, otherwise throws
+ * {@code NoSuchElementException}.
+ *
+ * @apiNote
+ * The methods {@link #orElse(long) orElse} and
+ * {@link #orElseGet(LongSupplier) orElseGet}
+ * are generally preferable to this method, as they return a substitute
+ * value if the value is absent, instead of throwing an exception.
+ *
+ * @return the value described by this {@code OptionalLong}
+ * @throws NoSuchElementException if no value is present
+ * @see OptionalLong#isPresent()
+ */
+ public long getAsLong() {
+ 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(LongConsumer 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(LongConsumer action, Runnable emptyAction) {
+ if (isPresent) {
+ action.accept(value);
+ } else {
+ emptyAction.run();
+ }
+ }
+
+ /**
+ * If a value is present, returns a sequential {@link LongStream} containing
+ * only that value, otherwise returns an empty {@code LongStream}.
+ *
+ * @apiNote
+ * This method can be used to transform a {@code Stream} of optional longs
+ * to an {@code LongStream} of present longs:
+ * <pre>{@code
+ * Stream<OptionalLong> os = ..
+ * LongStream s = os.flatMapToLong(OptionalLong::stream)
+ * }</pre>
+ *
+ * @return the optional value as an {@code LongStream}
+ * @since 9
+ */
+ public LongStream stream() {
+ if (isPresent) {
+ return LongStream.of(value);
+ } else {
+ return LongStream.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 long orElse(long 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 long orElseGet(LongSupplier supplier) {
+ return isPresent ? value : supplier.getAsLong();
+ }
+
+ /**
+ * 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> long 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 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 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 ? Long.hashCode(value) : 0;
+ }
+
+ /**
+ * Returns a non-empty string representation of this {@code OptionalLong}
+ * 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 OptionalLong}s must be
+ * unambiguously differentiable.
+ *
+ * @return the string representation of this instance
+ */
+ @Override
+ public String toString() {
+ return isPresent
+ ? String.format("OptionalLong[%s]", value)
+ : "OptionalLong.empty";
+ }
+}