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8080418: Add Optional.or()
Reviewed-by: chegar, forax, scolebourne
This commit is contained in:
Paul Sandoz
parent
46123d7fd5
commit
5e8d2b8ebd
5 changed files with 426 additions and 340 deletions
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@ -31,21 +31,22 @@ import java.util.function.Supplier;
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import java.util.stream.Stream;
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/**
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* A container object which may or may not contain a non-null value.
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* If a value is present, {@code isPresent()} will return {@code true} and
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* {@code get()} will return the value.
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* A container object which may or may not contain a non-{@code null} value.
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* If a value is present, {@code isPresent()} returns {@code true} and
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* {@code get()} 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(java.lang.Object) orElse()}
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* (return a default value if value not present) and
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* {@link #ifPresent(java.util.function.Consumer) ifPresent()} (perform an
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* action if the value is present).
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* (returns a default value if no value is present) and
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* {@link #ifPresent(java.util.function.Consumer) ifPresent()} (performs an
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* 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 Optional} may have unpredictable results and should be avoided.
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*
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* @param <T> the type of value
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* @since 1.8
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*/
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public final class Optional<T> {
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@ -71,14 +72,15 @@ public final class Optional<T> {
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/**
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* Returns an empty {@code Optional} instance. No value is present for this
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* Optional.
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* {@code Optional}.
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*
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* @apiNote Though it may be tempting to do so, avoid testing if an object
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* is empty by comparing with {@code ==} against instances returned by
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* {@code Option.empty()}. There is no guarantee that it is a singleton.
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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 Optional.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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* @param <T> Type of the non-existent value
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* @param <T> The type of the non-existent value
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* @return an empty {@code Optional}
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*/
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public static<T> Optional<T> empty() {
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@ -88,47 +90,47 @@ public final class Optional<T> {
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}
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/**
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* Constructs an instance with the value present.
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* Constructs an instance with the described value.
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*
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* @param value the non-null value to be present
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* @throws NullPointerException if value is null
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* @param value the non-{@code null} value to describe
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* @throws NullPointerException if value is {@code null}
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*/
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private Optional(T value) {
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this.value = Objects.requireNonNull(value);
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}
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/**
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* Returns an {@code Optional} with the specified present non-null value.
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* Returns an {@code Optional} describing the given non-{@code null}
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* value.
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*
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* @param <T> the class of the value
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* @param value the value to be present, which must be non-null
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* @param value the value to describe, which must be non-{@code null}
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* @param <T> the type of the value
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* @return an {@code Optional} with the value present
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* @throws NullPointerException if value is null
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* @throws NullPointerException if value is {@code null}
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*/
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public static <T> Optional<T> of(T value) {
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return new Optional<>(value);
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}
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/**
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* Returns an {@code Optional} describing the specified value, if non-null,
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* otherwise returns an empty {@code Optional}.
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* Returns an {@code Optional} describing the given value, if
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* non-{@code null}, otherwise returns an empty {@code Optional}.
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*
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* @param <T> the class of the value
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* @param value the possibly-null value to describe
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* @param value the possibly-{@code null} value to describe
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* @param <T> the type of the value
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* @return an {@code Optional} with a present value if the specified value
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* is non-null, otherwise an empty {@code Optional}
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* is non-{@code null}, otherwise an empty {@code Optional}
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*/
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public static <T> Optional<T> ofNullable(T value) {
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return value == null ? empty() : of(value);
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}
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/**
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* If a value is present in this {@code Optional}, returns the value,
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* otherwise throws {@code NoSuchElementException}.
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*
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* @return the non-null value held by this {@code Optional}
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* @throws NoSuchElementException if there is no value present
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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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* @return the non-{@code null} value described by this {@code Optional}
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* @throws NoSuchElementException if no value is present
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* @see Optional#isPresent()
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*/
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public T get() {
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@ -139,21 +141,21 @@ public final class Optional<T> {
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}
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/**
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* Return {@code true} if there is a value present, otherwise {@code false}.
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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 there is a value present, otherwise {@code false}
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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 value != null;
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}
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/**
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* If a value is present, perform the given action with the value,
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* otherwise do nothing.
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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 a value is present and {@code action} is
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* null
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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(Consumer<? super T> action) {
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if (value != null) {
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@ -162,15 +164,16 @@ public final class Optional<T> {
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}
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/**
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* If a value is present, perform the given action with the value,
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* otherwise perform the given empty-based action.
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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 a value is
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* not present
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* @throws NullPointerException if a value is present and {@code action} is
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* null, or a value is not present and {@code emptyAction} is null.
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* @since 1.9
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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(Consumer<? super T> action, Runnable emptyAction) {
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if (value != null) {
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@ -182,14 +185,14 @@ public final class Optional<T> {
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/**
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* If a value is present, and the value matches the given predicate,
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* return an {@code Optional} describing the value, otherwise return an
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* returns an {@code Optional} describing the value, otherwise returns an
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* empty {@code Optional}.
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*
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* @param predicate a predicate to apply to the value, if present
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* @return an {@code Optional} describing the value of this {@code Optional}
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* if a value is present and the value matches the given predicate,
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* otherwise an empty {@code Optional}
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* @throws NullPointerException if the predicate is null
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* @param predicate the predicate to apply to a value, if present
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* @return an {@code Optional} describing the value of this
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* {@code Optional}, if a value is present and the value matches the
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* given predicate, otherwise an empty {@code Optional}
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* @throws NullPointerException if the predicate is {@code null}
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*/
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public Optional<T> filter(Predicate<? super T> predicate) {
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Objects.requireNonNull(predicate);
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@ -201,14 +204,18 @@ public final class Optional<T> {
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}
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/**
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* If a value is present, apply the provided mapping function to it,
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* and if the result is non-null, return an {@code Optional} describing the
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* result. Otherwise return an empty {@code Optional}.
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* If a value is present, returns an {@code Optional} describing (as if by
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* {@link #ofNullable}) the result of applying the given mapping function to
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* the value, otherwise returns an empty {@code Optional}.
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*
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* @apiNote This method supports post-processing on optional values, without
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* <p>If the mapping function returns a {@code null} result then this method
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* returns an empty {@code Optional}.
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*
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* @apiNote
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* This method supports post-processing on {@code Optional} values, without
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* the need to explicitly check for a return status. For example, the
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* following code traverses a stream of file names, selects one that has
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* not yet been processed, and then opens that file, returning an
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* following code traverses a stream of file names, selects one that has not
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* yet been processed, and then opens that file, returning an
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* {@code Optional<FileInputStream>}:
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*
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* <pre>{@code
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@ -222,12 +229,12 @@ public final class Optional<T> {
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* {@code map} returns an {@code Optional<FileInputStream>} for the desired
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* file if one exists.
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*
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* @param <U> The type of the result of the mapping function
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* @param mapper a mapping function to apply to the value, if present
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* @param mapper the mapping function to apply to a value, if present
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* @param <U> The type of the value returned from the mapping function
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* @return an {@code Optional} describing the result of applying a mapping
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* function to the value of this {@code Optional}, if a value is present,
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* otherwise an empty {@code Optional}
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* @throws NullPointerException if the mapping function is null
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* function to the value of this {@code Optional}, if a value is
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* present, otherwise an empty {@code Optional}
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* @throws NullPointerException if the mapping function is {@code null}
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*/
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public<U> Optional<U> map(Function<? super T, ? extends U> mapper) {
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Objects.requireNonNull(mapper);
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@ -239,21 +246,23 @@ public final class Optional<T> {
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}
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/**
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* If a value is present, apply the provided {@code Optional}-bearing
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* mapping function to it, return that result, otherwise return an empty
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* {@code Optional}. This method is similar to {@link #map(Function)},
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* but the provided mapper is one whose result is already an {@code Optional},
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* and if invoked, {@code flatMap} does not wrap it with an additional
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* If a value is present, returns the result of applying the given
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* {@code Optional}-bearing mapping function to the value, otherwise returns
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* an empty {@code Optional}.
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*
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* <p>This method is similar to {@link #map(Function)}, but the mapping
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* function is one whose result is already an {@code Optional}, and if
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* invoked, {@code flatMap} does not wrap it within an additional
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* {@code Optional}.
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*
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* @param <U> The type parameter to the {@code Optional} returned by
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* @param mapper a mapping function to apply to the value, if present
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* the mapping function
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* @param <U> The type of value of the {@code Optional} returned by the
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* mapping function
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* @param mapper the mapping function to apply to a value, if present
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* @return the result of applying an {@code Optional}-bearing mapping
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* function to the value of this {@code Optional}, if a value is present,
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* otherwise an empty {@code Optional}
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* @throws NullPointerException if the mapping function is null or returns
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* a null result
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* function to the value of this {@code Optional}, if a value is
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* present, otherwise an empty {@code Optional}
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* @throws NullPointerException if the mapping function is {@code null} or
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* returns a {@code null} result
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*/
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public<U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) {
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Objects.requireNonNull(mapper);
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@ -265,19 +274,41 @@ public final class Optional<T> {
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}
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/**
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* If a value is present return a sequential {@link Stream} containing only
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* that value, otherwise return an empty {@code Stream}.
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* If a value is present, returns an {@code Optional} describing the value,
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* otherwise returns an {@code Optional} produced by the supplying function.
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*
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* @apiNote This method can be used to transform a {@code Stream} of
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* optional elements to a {@code Stream} of present value elements:
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* @param supplier the supplying function that produces an {@code Optional}
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* to be returned
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* @return returns an {@code Optional} describing the value of this
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* {@code Optional}, if a value is present, otherwise an
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* {@code Optional} produced by the supplying function.
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* @throws NullPointerException if the supplying function is {@code null} or
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* produces a {@code null} result
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* @since 9
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*/
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public Optional<T> or(Supplier<Optional<T>> supplier) {
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Objects.requireNonNull(supplier);
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if (isPresent()) {
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return this;
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} else {
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return Objects.requireNonNull(supplier.get());
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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 Stream} containing
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* only that value, otherwise returns an empty {@code Stream}.
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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
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* elements to a {@code Stream} of present value elements:
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* <pre>{@code
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* Stream<Optional<T>> os = ..
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* Stream<T> s = os.flatMap(Optional::stream)
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* }</pre>
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*
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* @return the optional value as a {@code Stream}
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* @since 1.9
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* @since 9
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*/
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public Stream<T> stream() {
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if (!isPresent()) {
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@ -288,10 +319,11 @@ public final class Optional<T> {
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}
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/**
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* Return the value if present, otherwise return {@code other}.
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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 there is no value present, may
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* be null
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* @param other the value to be returned, if no value is present.
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* May be {@code null}.
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* @return the value, if present, otherwise {@code other}
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*/
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public T orElse(T other) {
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@ -299,34 +331,35 @@ public final class Optional<T> {
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}
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/**
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* Return the value if present, otherwise invoke {@code other} and return
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* the result of that invocation.
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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 other a {@code Supplier} whose result is returned if no value
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* is present
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* @return the value if present otherwise the result of {@code other.get()}
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* @throws NullPointerException if value is not present and {@code other} is
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* null
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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 T orElseGet(Supplier<? extends T> other) {
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return value != null ? value : other.get();
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public T orElseGet(Supplier<? extends T> supplier) {
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return value != null ? value : supplier.get();
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}
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/**
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* Return the contained value, if present, otherwise throw an exception
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* to be created by the provided supplier.
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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 A method reference to the exception constructor with an empty
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* argument list can be used as the supplier. For example,
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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 supplier which will return the exception to
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* be thrown
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* @return the present value
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* @throws X if there is no value present
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* @throws NullPointerException if no value is present and
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* {@code exceptionSupplier} is null
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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> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
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if (value != null) {
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@ -337,8 +370,8 @@ public final class Optional<T> {
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}
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/**
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* Indicates whether some other object is "equal to" this Optional. The
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* other object is considered equal if:
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* Indicates whether some other object is "equal to" this {@code Optional}.
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* The other object is considered equal if:
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* <ul>
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* <li>it is also an {@code Optional} and;
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* <li>both instances have no value present or;
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@ -347,7 +380,7 @@ public final class Optional<T> {
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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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* 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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@ -364,10 +397,11 @@ public final class Optional<T> {
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}
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/**
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* Returns the hash code value of the present value, if any, or 0 (zero) if
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* no value is present.
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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 0 if no value is present
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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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@ -375,13 +409,14 @@ public final class Optional<T> {
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}
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/**
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* Returns a non-empty string representation of this Optional suitable for
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* debugging. The exact presentation format is unspecified and may vary
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* between implementations and versions.
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* Returns a non-empty string representation of this {@code Optional}
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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 If a value is present the result must include its string
|
||||
* representation in the result. Empty and present Optionals must be
|
||||
* unambiguously differentiable.
|
||||
* @implSpec
|
||||
* If a value is present the result must include its string representation
|
||||
* in the result. Empty and present {@code Optional}s must be unambiguously
|
||||
* differentiable.
|
||||
*
|
||||
* @return the string representation of this instance
|
||||
*/
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue