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25 package java.util;
26 
27 import java.util.function.LongConsumer;
28 import java.util.function.LongSupplier;
29 import java.util.function.Supplier;
30 
31 // Android-changed: removed ValueBased paragraph.
32 /**
33  * A container object which may or may not contain a {@code long} value.
34  * If a value is present, {@code isPresent()} will return {@code true} and
35  * {@code getAsLong()} will return the value.
36  *
37  * <p>Additional methods that depend on the presence or absence of a contained
38  * value are provided, such as {@link #orElse(long) orElse()}
39  * (return a default value if value not present) and
40  * {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (execute a block
41  * of code if the value is present).
42  *
43  * @since 1.8
44  */
45 public final class OptionalLong {
46     /**
47      * Common instance for {@code empty()}.
48      */
49     private static final OptionalLong EMPTY = new OptionalLong();
50 
51     /**
52      * If true then the value is present, otherwise indicates no value is present
53      */
54     private final boolean isPresent;
55     private final long value;
56 
57     /**
58      * Construct an empty instance.
59      *
60      * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
61      * should exist per VM.
62      */
OptionalLong()63     private OptionalLong() {
64         this.isPresent = false;
65         this.value = 0;
66     }
67 
68     /**
69      * Returns an empty {@code OptionalLong} instance.  No value is present for this
70      * OptionalLong.
71      *
72      * @apiNote Though it may be tempting to do so, avoid testing if an object
73      * is empty by comparing with {@code ==} against instances returned by
74      * {@code Option.empty()}. There is no guarantee that it is a singleton.
75      * Instead, use {@link #isPresent()}.
76      *
77      *  @return an empty {@code OptionalLong}.
78      */
empty()79     public static OptionalLong empty() {
80         return EMPTY;
81     }
82 
83     /**
84      * Construct an instance with the value present.
85      *
86      * @param value the long value to be present
87      */
OptionalLong(long value)88     private OptionalLong(long value) {
89         this.isPresent = true;
90         this.value = value;
91     }
92 
93     /**
94      * Return an {@code OptionalLong} with the specified value present.
95      *
96      * @param value the value to be present
97      * @return an {@code OptionalLong} with the value present
98      */
of(long value)99     public static OptionalLong of(long value) {
100         return new OptionalLong(value);
101     }
102 
103     /**
104      * If a value is present in this {@code OptionalLong}, returns the value,
105      * otherwise throws {@code NoSuchElementException}.
106      *
107      * @return the value held by this {@code OptionalLong}
108      * @throws NoSuchElementException if there is no value present
109      *
110      * @see OptionalLong#isPresent()
111      */
getAsLong()112     public long getAsLong() {
113         if (!isPresent) {
114             throw new NoSuchElementException("No value present");
115         }
116         return value;
117     }
118 
119     /**
120      * Return {@code true} if there is a value present, otherwise {@code false}.
121      *
122      * @return {@code true} if there is a value present, otherwise {@code false}
123      */
isPresent()124     public boolean isPresent() {
125         return isPresent;
126     }
127 
128     /**
129      * Have the specified consumer accept the value if a value is present,
130      * otherwise do nothing.
131      *
132      * @param consumer block to be executed if a value is present
133      * @throws NullPointerException if value is present and {@code consumer} is
134      * null
135      */
ifPresent(LongConsumer consumer)136     public void ifPresent(LongConsumer consumer) {
137         if (isPresent)
138             consumer.accept(value);
139     }
140 
141     /**
142      * Return the value if present, otherwise return {@code other}.
143      *
144      * @param other the value to be returned if there is no value present
145      * @return the value, if present, otherwise {@code other}
146      */
orElse(long other)147     public long orElse(long other) {
148         return isPresent ? value : other;
149     }
150 
151     /**
152      * Return the value if present, otherwise invoke {@code other} and return
153      * the result of that invocation.
154      *
155      * @param other a {@code LongSupplier} whose result is returned if no value
156      * is present
157      * @return the value if present otherwise the result of {@code other.getAsLong()}
158      * @throws NullPointerException if value is not present and {@code other} is
159      * null
160      */
orElseGet(LongSupplier other)161     public long orElseGet(LongSupplier other) {
162         return isPresent ? value : other.getAsLong();
163     }
164 
165     /**
166      * Return the contained value, if present, otherwise throw an exception
167      * to be created by the provided supplier.
168      *
169      * @apiNote A method reference to the exception constructor with an empty
170      * argument list can be used as the supplier. For example,
171      * {@code IllegalStateException::new}
172      *
173      * @param <X> Type of the exception to be thrown
174      * @param exceptionSupplier The supplier which will return the exception to
175      * be thrown
176      * @return the present value
177      * @throws X if there is no value present
178      * @throws NullPointerException if no value is present and
179      * {@code exceptionSupplier} is null
180      */
orElseThrow(Supplier<X> exceptionSupplier)181     public<X extends Throwable> long orElseThrow(Supplier<X> exceptionSupplier) throws X {
182         if (isPresent) {
183             return value;
184         } else {
185             throw exceptionSupplier.get();
186         }
187     }
188 
189     /**
190      * Indicates whether some other object is "equal to" this OptionalLong. The
191      * other object is considered equal if:
192      * <ul>
193      * <li>it is also an {@code OptionalLong} and;
194      * <li>both instances have no value present or;
195      * <li>the present values are "equal to" each other via {@code ==}.
196      * </ul>
197      *
198      * @param obj an object to be tested for equality
199      * @return {code true} if the other object is "equal to" this object
200      * otherwise {@code false}
201      */
202     @Override
equals(Object obj)203     public boolean equals(Object obj) {
204         if (this == obj) {
205             return true;
206         }
207 
208         if (!(obj instanceof OptionalLong)) {
209             return false;
210         }
211 
212         OptionalLong other = (OptionalLong) obj;
213         return (isPresent && other.isPresent)
214                 ? value == other.value
215                 : isPresent == other.isPresent;
216     }
217 
218     /**
219      * Returns the hash code value of the present value, if any, or 0 (zero) if
220      * no value is present.
221      *
222      * @return hash code value of the present value or 0 if no value is present
223      */
224     @Override
hashCode()225     public int hashCode() {
226         return isPresent ? Long.hashCode(value) : 0;
227     }
228 
229     /**
230      * {@inheritDoc}
231      *
232      * Returns a non-empty string representation of this object suitable for
233      * debugging. The exact presentation format is unspecified and may vary
234      * between implementations and versions.
235      *
236      * @implSpec If a value is present the result must include its string
237      * representation in the result. Empty and present instances must be
238      * unambiguously differentiable.
239      *
240      * @return the string representation of this instance
241      */
242     @Override
toString()243     public String toString() {
244         return isPresent
245                 ? String.format("OptionalLong[%s]", value)
246                 : "OptionalLong.empty";
247     }
248 }
249