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). * *
This is a value-based
* 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