-package org.simantics.db.function;\r
-\r
-import java.util.NoSuchElementException;\r
-import java.util.Objects;\r
-\r
-import org.simantics.db.exception.DatabaseException;\r
-\r
-/**\r
- * A container object which may or may not contain a non-null value. If a value\r
- * is present, {@code isPresent()} will return {@code true} and {@code get()}\r
- * will return the value.\r
- *\r
- * <p>\r
- * Additional methods that depend on the presence or absence of a contained\r
- * value are provided, such as {@link #orElse(java.lang.Object) orElse()}\r
- * (return a default value if value not present) and\r
- * {@link #ifPresent(org.simantics.db.function.DbConsumer) ifPresent()} (execute\r
- * a block of code if the value is present).\r
- *\r
- * <p>\r
- * This is a value-based class; use of identity-sensitive operations (including\r
- * reference equality ({@code ==}), identity hash code, or synchronization) on\r
- * instances of {@code DbOptional} may have unpredictable results and should be\r
- * avoided.\r
- *\r
- * @since 1.25\r
- */\r
-public final class DbOptional<T> {\r
- /**\r
- * Common instance for {@code empty()}.\r
- */\r
- private static final DbOptional<?> EMPTY = new DbOptional<>();\r
-\r
- /**\r
- * If non-null, the value; if null, indicates no value is present\r
- */\r
- private final T value;\r
-\r
- /**\r
- * Constructs an empty instance.\r
- *\r
- * @implNote Generally only one empty instance, {@link Optional#EMPTY},\r
- * should exist per VM.\r
- */\r
- private DbOptional() {\r
- this.value = null;\r
- }\r
-\r
- /**\r
- * Returns an empty {@code Optional} instance. No value is present for this\r
- * Optional.\r
- *\r
- * @apiNote Though it may be tempting to do so, avoid testing if an object\r
- * is empty by comparing with {@code ==} against instances returned by\r
- * {@code Option.empty()}. There is no guarantee that it is a singleton.\r
- * Instead, use {@link #isPresent()}.\r
- *\r
- * @param <T> Type of the non-existent value\r
- * @return an empty {@code Optional}\r
- */\r
- public static<T> DbOptional<T> empty() {\r
- @SuppressWarnings("unchecked")\r
- DbOptional<T> t = (DbOptional<T>) EMPTY;\r
- return t;\r
- }\r
-\r
- /**\r
- * Constructs an instance with the value present.\r
- *\r
- * @param value the non-null value to be present\r
- * @throws NullPointerException if value is null\r
- */\r
- private DbOptional(T value) {\r
- this.value = Objects.requireNonNull(value);\r
- }\r
-\r
- /**\r
- * Returns an {@code Optional} with the specified present non-null value.\r
- *\r
- * @param <T> the class of the value\r
- * @param value the value to be present, which must be non-null\r
- * @return an {@code Optional} with the value present\r
- * @throws NullPointerException if value is null\r
- */\r
- public static <T> DbOptional<T> of(T value) {\r
- return new DbOptional<>(value);\r
- }\r
-\r
- /**\r
- * Returns an {@code Optional} describing the specified value, if non-null,\r
- * otherwise returns an empty {@code Optional}.\r
- *\r
- * @param <T> the class of the value\r
- * @param value the possibly-null value to describe\r
- * @return an {@code Optional} with a present value if the specified value\r
- * is non-null, otherwise an empty {@code Optional}\r
- */\r
- public static <T> DbOptional<T> ofNullable(T value) {\r
- return value == null ? empty() : of(value);\r
- }\r
-\r
- /**\r
- * If a value is present in this {@code Optional}, returns the value,\r
- * otherwise throws {@code NoSuchElementException}.\r
- *\r
- * @return the non-null value held by this {@code Optional}\r
- * @throws NoSuchElementException if there is no value present\r
- *\r
- * @see Optional#isPresent()\r
- */\r
- public T get() {\r
- if (value == null) {\r
- throw new NoSuchElementException("No value present");\r
- }\r
- return value;\r
- }\r
-\r
- /**\r
- * Return {@code true} if there is a value present, otherwise {@code false}.\r
- *\r
- * @return {@code true} if there is a value present, otherwise {@code false}\r
- */\r
- public boolean isPresent() {\r
- return value != null;\r
- }\r
-\r
- /**\r
- * If a value is present, invoke the specified consumer with the value,\r
- * otherwise do nothing.\r
- *\r
- * @param consumer block to be executed if a value is present\r
- * @throws DatabaseException \r
- * @throws NullPointerException if value is present and {@code consumer} is\r
- * null\r
- */\r
- public void ifPresent(DbConsumer<? super T> consumer) throws DatabaseException {\r
- if (value != null)\r
- consumer.accept(value);\r
- }\r
-\r
- /**\r
- * If a value is present, and the value matches the given predicate,\r
- * return an {@code Optional} describing the value, otherwise return an\r
- * empty {@code Optional}.\r
- *\r
- * @param predicate a predicate to apply to the value, if present\r
- * @return an {@code Optional} describing the value of this {@code Optional}\r
- * if a value is present and the value matches the given predicate,\r
- * otherwise an empty {@code Optional}\r
- * @throws DatabaseException \r
- * @throws NullPointerException if the predicate is null\r
- */\r
- public DbOptional<T> filter(DbPredicate<? super T> predicate) throws DatabaseException {\r
- Objects.requireNonNull(predicate);\r
- if (!isPresent())\r
- return this;\r
- else\r
- return predicate.test(value) ? this : empty();\r
- }\r
-\r
- /**\r
- * If a value is present, apply the provided mapping function to it,\r
- * and if the result is non-null, return an {@code Optional} describing the\r
- * result. Otherwise return an empty {@code Optional}.\r
- *\r
- * @apiNote This method supports post-processing on optional values, without\r
- * the need to explicitly check for a return status. For example, the\r
- * following code traverses a stream of file names, selects one that has\r
- * not yet been processed, and then opens that file, returning an\r
- * {@code Optional<FileInputStream>}:\r
- *\r
- * <pre>{@code\r
- * Optional<FileInputStream> fis =\r
- * names.stream().filter(name -> !isProcessedYet(name))\r
- * .findFirst()\r
- * .map(name -> new FileInputStream(name));\r
- * }</pre>\r
- *\r
- * Here, {@code findFirst} returns an {@code Optional<String>}, and then\r
- * {@code map} returns an {@code Optional<FileInputStream>} for the desired\r
- * file if one exists.\r
- *\r
- * @param <U> The type of the result of the mapping function\r
- * @param mapper a mapping function to apply to the value, if present\r
- * @return an {@code Optional} describing the result of applying a mapping\r
- * function to the value of this {@code Optional}, if a value is present,\r
- * otherwise an empty {@code Optional}\r
- * @throws DatabaseException \r
- * @throws NullPointerException if the mapping function is null\r
- */\r
- public<U> DbOptional<U> map(DbFunction<? super T, ? extends U> mapper) throws DatabaseException {\r
- Objects.requireNonNull(mapper);\r
- if (!isPresent())\r
- return empty();\r
- else {\r
- return DbOptional.ofNullable(mapper.apply(value));\r
- }\r
- }\r
-\r
- /**\r
- * If a value is present, apply the provided {@code Optional}-bearing\r
- * mapping function to it, return that result, otherwise return an empty\r
- * {@code Optional}. This method is similar to {@link #map(Function)},\r
- * but the provided mapper is one whose result is already an {@code Optional},\r
- * and if invoked, {@code flatMap} does not wrap it with an additional\r
- * {@code Optional}.\r
- *\r
- * @param <U> The type parameter to the {@code Optional} returned by\r
- * @param mapper a mapping function to apply to the value, if present\r
- * the mapping function\r
- * @return the result of applying an {@code Optional}-bearing mapping\r
- * function to the value of this {@code Optional}, if a value is present,\r
- * otherwise an empty {@code Optional}\r
- * @throws DatabaseException \r
- * @throws NullPointerException if the mapping function is null or returns\r
- * a null result\r
- */\r
- public<U> DbOptional<U> flatMap(DbFunction<? super T, DbOptional<U>> mapper) throws DatabaseException {\r
- Objects.requireNonNull(mapper);\r
- if (!isPresent())\r
- return empty();\r
- else {\r
- return Objects.requireNonNull(mapper.apply(value));\r
- }\r
- }\r
-\r
- /**\r
- * Return the value if present, otherwise return {@code other}.\r
- *\r
- * @param other the value to be returned if there is no value present, may\r
- * be null\r
- * @return the value, if present, otherwise {@code other}\r
- */\r
- public T orElse(T other) {\r
- return value != null ? value : other;\r
- }\r
-\r
- /**\r
- * Return the value if present, otherwise invoke {@code other} and return\r
- * the result of that invocation.\r
- *\r
- * @param other a {@code Supplier} whose result is returned if no value\r
- * is present\r
- * @return the value if present otherwise the result of {@code other.get()}\r
- * @throws DatabaseException \r
- * @throws NullPointerException if value is not present and {@code other} is\r
- * null\r
- */\r
- public T orElseGet(DbSupplier<? extends T> other) throws DatabaseException {\r
- return value != null ? value : other.get();\r
- }\r
-\r
- /**\r
- * Return the contained value, if present, otherwise throw an exception\r
- * to be created by the provided supplier.\r
- *\r
- * @apiNote A method reference to the exception constructor with an empty\r
- * argument list can be used as the supplier. For example,\r
- * {@code IllegalStateException::new}\r
- *\r
- * @param <X> Type of the exception to be thrown\r
- * @param exceptionSupplier The supplier which will return the exception to\r
- * be thrown\r
- * @return the present value\r
- * @throws X if there is no value present\r
- * @throws DatabaseException \r
- * @throws NullPointerException if no value is present and\r
- * {@code exceptionSupplier} is null\r
- */\r
- public <X extends Throwable> T orElseThrow(DbSupplier<? extends X> exceptionSupplier) throws X, DatabaseException {\r
- if (value != null) {\r
- return value;\r
- } else {\r
- throw exceptionSupplier.get();\r
- }\r
- }\r
-\r
- /**\r
- * Indicates whether some other object is "equal to" this Optional. The\r
- * other object is considered equal if:\r
- * <ul>\r
- * <li>it is also an {@code Optional} and;\r
- * <li>both instances have no value present or;\r
- * <li>the present values are "equal to" each other via {@code equals()}.\r
- * </ul>\r
- *\r
- * @param obj an object to be tested for equality\r
- * @return {code true} if the other object is "equal to" this object\r
- * otherwise {@code false}\r
- */\r
- @Override\r
- public boolean equals(Object obj) {\r
- if (this == obj) {\r
- return true;\r
- }\r
-\r
- if (!(obj instanceof DbOptional)) {\r
- return false;\r
- }\r
-\r
- DbOptional<?> other = (DbOptional<?>) obj;\r
- return Objects.equals(value, other.value);\r
- }\r
-\r
- /**\r
- * Returns the hash code value of the present value, if any, or 0 (zero) if\r
- * no value is present.\r
- *\r
- * @return hash code value of the present value or 0 if no value is present\r
- */\r
- @Override\r
- public int hashCode() {\r
- return Objects.hashCode(value);\r
- }\r
-\r
- /**\r
- * Returns a non-empty string representation of this Optional suitable for\r
- * debugging. The exact presentation format is unspecified and may vary\r
- * between implementations and versions.\r
- *\r
- * @implSpec If a value is present the result must include its string\r
- * representation in the result. Empty and present DbOptionals must be\r
- * unambiguously differentiable.\r
- *\r
- * @return the string representation of this instance\r
- */\r
- @Override\r
- public String toString() {\r
- return value != null\r
- ? String.format("DbOptional[%s]", value)\r
- : "DbOptional.empty";\r
- }\r
-}\r
+package org.simantics.db.function;
+
+import java.util.NoSuchElementException;
+import java.util.Objects;
+
+import org.simantics.db.exception.DatabaseException;
+
+/**
+ * A container object which may or may not contain a non-null value. If a value
+ * is present, {@code isPresent()} will return {@code true} and {@code get()}
+ * will return the value.
+ *
+ * <p>
+ * Additional methods that depend on the presence or absence of a contained
+ * value are provided, such as {@link #orElse(java.lang.Object) orElse()}
+ * (return a default value if value not present) and
+ * {@link #ifPresent(org.simantics.db.function.DbConsumer) ifPresent()} (execute
+ * a block of code if the value is present).
+ *
+ * <p>
+ * This is a value-based class; use of identity-sensitive operations (including
+ * reference equality ({@code ==}), identity hash code, or synchronization) on
+ * instances of {@code DbOptional} may have unpredictable results and should be
+ * avoided.
+ *
+ * @since 1.25
+ */
+public final class DbOptional<T> {
+ /**
+ * Common instance for {@code empty()}.
+ */
+ private static final DbOptional<?> EMPTY = new DbOptional<>();
+
+ /**
+ * If non-null, the value; if null, indicates no value is present
+ */
+ private final T value;
+
+ /**
+ * Constructs an empty instance.
+ *
+ * @implNote Generally only one empty instance, {@link Optional#EMPTY},
+ * should exist per VM.
+ */
+ private DbOptional() {
+ this.value = null;
+ }
+
+ /**
+ * Returns an empty {@code Optional} instance. No value is present for this
+ * Optional.
+ *
+ * @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()}.
+ *
+ * @param <T> Type of the non-existent value
+ * @return an empty {@code Optional}
+ */
+ public static<T> DbOptional<T> empty() {
+ @SuppressWarnings("unchecked")
+ DbOptional<T> t = (DbOptional<T>) EMPTY;
+ return t;
+ }
+
+ /**
+ * Constructs an instance with the value present.
+ *
+ * @param value the non-null value to be present
+ * @throws NullPointerException if value is null
+ */
+ private DbOptional(T value) {
+ this.value = Objects.requireNonNull(value);
+ }
+
+ /**
+ * Returns an {@code Optional} with the specified present non-null value.
+ *
+ * @param <T> the class of the value
+ * @param value the value to be present, which must be non-null
+ * @return an {@code Optional} with the value present
+ * @throws NullPointerException if value is null
+ */
+ public static <T> DbOptional<T> of(T value) {
+ return new DbOptional<>(value);
+ }
+
+ /**
+ * Returns an {@code Optional} describing the specified value, if non-null,
+ * otherwise returns an empty {@code Optional}.
+ *
+ * @param <T> the class of the value
+ * @param value the possibly-null value to describe
+ * @return an {@code Optional} with a present value if the specified value
+ * is non-null, otherwise an empty {@code Optional}
+ */
+ public static <T> DbOptional<T> ofNullable(T value) {
+ return value == null ? empty() : of(value);
+ }
+
+ /**
+ * If a value is present in this {@code Optional}, returns the value,
+ * otherwise throws {@code NoSuchElementException}.
+ *
+ * @return the non-null value held by this {@code Optional}
+ * @throws NoSuchElementException if there is no value present
+ *
+ * @see Optional#isPresent()
+ */
+ public T get() {
+ if (value == null) {
+ 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 value != null;
+ }
+
+ /**
+ * If a value is present, invoke the specified consumer with the value,
+ * otherwise do nothing.
+ *
+ * @param consumer block to be executed if a value is present
+ * @throws DatabaseException
+ * @throws NullPointerException if value is present and {@code consumer} is
+ * null
+ */
+ public void ifPresent(DbConsumer<? super T> consumer) throws DatabaseException {
+ if (value != null)
+ consumer.accept(value);
+ }
+
+ /**
+ * If a value is present, and the value matches the given predicate,
+ * return an {@code Optional} describing the value, otherwise return an
+ * empty {@code Optional}.
+ *
+ * @param predicate a predicate to apply to the value, if present
+ * @return an {@code Optional} describing the value of this {@code Optional}
+ * if a value is present and the value matches the given predicate,
+ * otherwise an empty {@code Optional}
+ * @throws DatabaseException
+ * @throws NullPointerException if the predicate is null
+ */
+ public DbOptional<T> filter(DbPredicate<? super T> predicate) throws DatabaseException {
+ Objects.requireNonNull(predicate);
+ if (!isPresent())
+ return this;
+ else
+ return predicate.test(value) ? this : empty();
+ }
+
+ /**
+ * If a value is present, apply the provided mapping function to it,
+ * and if the result is non-null, return an {@code Optional} describing the
+ * result. Otherwise return an empty {@code Optional}.
+ *
+ * @apiNote This method supports post-processing on optional values, without
+ * the need to explicitly check for a return status. For example, the
+ * following code traverses a stream of file names, selects one that has
+ * not yet been processed, and then opens that file, returning an
+ * {@code Optional<FileInputStream>}:
+ *
+ * <pre>{@code
+ * Optional<FileInputStream> fis =
+ * names.stream().filter(name -> !isProcessedYet(name))
+ * .findFirst()
+ * .map(name -> new FileInputStream(name));
+ * }</pre>
+ *
+ * Here, {@code findFirst} returns an {@code Optional<String>}, and then
+ * {@code map} returns an {@code Optional<FileInputStream>} for the desired
+ * file if one exists.
+ *
+ * @param <U> The type of the result of the mapping function
+ * @param mapper a mapping function to apply to the value, if present
+ * @return an {@code Optional} describing the result of applying a mapping
+ * function to the value of this {@code Optional}, if a value is present,
+ * otherwise an empty {@code Optional}
+ * @throws DatabaseException
+ * @throws NullPointerException if the mapping function is null
+ */
+ public<U> DbOptional<U> map(DbFunction<? super T, ? extends U> mapper) throws DatabaseException {
+ Objects.requireNonNull(mapper);
+ if (!isPresent())
+ return empty();
+ else {
+ return DbOptional.ofNullable(mapper.apply(value));
+ }
+ }
+
+ /**
+ * If a value is present, apply the provided {@code Optional}-bearing
+ * mapping function to it, return that result, otherwise return an empty
+ * {@code Optional}. This method is similar to {@link #map(Function)},
+ * but the provided mapper is one whose result is already an {@code Optional},
+ * and if invoked, {@code flatMap} does not wrap it with an additional
+ * {@code Optional}.
+ *
+ * @param <U> The type parameter to the {@code Optional} returned by
+ * @param mapper a mapping function to apply to the value, if present
+ * the mapping function
+ * @return the result of applying an {@code Optional}-bearing mapping
+ * function to the value of this {@code Optional}, if a value is present,
+ * otherwise an empty {@code Optional}
+ * @throws DatabaseException
+ * @throws NullPointerException if the mapping function is null or returns
+ * a null result
+ */
+ public<U> DbOptional<U> flatMap(DbFunction<? super T, DbOptional<U>> mapper) throws DatabaseException {
+ Objects.requireNonNull(mapper);
+ if (!isPresent())
+ return empty();
+ else {
+ return Objects.requireNonNull(mapper.apply(value));
+ }
+ }
+
+ /**
+ * Return the value if present, otherwise return {@code other}.
+ *
+ * @param other the value to be returned if there is no value present, may
+ * be null
+ * @return the value, if present, otherwise {@code other}
+ */
+ public T orElse(T other) {
+ return value != null ? value : other;
+ }
+
+ /**
+ * Return the value if present, otherwise invoke {@code other} and return
+ * the result of that invocation.
+ *
+ * @param other a {@code Supplier} whose result is returned if no value
+ * is present
+ * @return the value if present otherwise the result of {@code other.get()}
+ * @throws DatabaseException
+ * @throws NullPointerException if value is not present and {@code other} is
+ * null
+ */
+ public T orElseGet(DbSupplier<? extends T> other) throws DatabaseException {
+ return value != null ? value : other.get();
+ }
+
+ /**
+ * 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 <X> Type of the exception to be thrown
+ * @param exceptionSupplier The supplier which will return the exception to
+ * be thrown
+ * @return the present value
+ * @throws X if there is no value present
+ * @throws DatabaseException
+ * @throws NullPointerException if no value is present and
+ * {@code exceptionSupplier} is null
+ */
+ public <X extends Throwable> T orElseThrow(DbSupplier<? extends X> exceptionSupplier) throws X, DatabaseException {
+ if (value != null) {
+ return value;
+ } else {
+ throw exceptionSupplier.get();
+ }
+ }
+
+ /**
+ * Indicates whether some other object is "equal to" this Optional. The
+ * other object is considered equal if:
+ * <ul>
+ * <li>it is also an {@code Optional} and;
+ * <li>both instances have no value present or;
+ * <li>the present values are "equal to" each other via {@code equals()}.
+ * </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 DbOptional)) {
+ return false;
+ }
+
+ DbOptional<?> other = (DbOptional<?>) obj;
+ return Objects.equals(value, other.value);
+ }
+
+ /**
+ * Returns the hash code value of the present value, if any, or 0 (zero) if
+ * no value is present.
+ *
+ * @return hash code value of the present value or 0 if no value is present
+ */
+ @Override
+ public int hashCode() {
+ return Objects.hashCode(value);
+ }
+
+ /**
+ * Returns a non-empty string representation of this Optional 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 DbOptionals must be
+ * unambiguously differentiable.
+ *
+ * @return the string representation of this instance
+ */
+ @Override
+ public String toString() {
+ return value != null
+ ? String.format("DbOptional[%s]", value)
+ : "DbOptional.empty";
+ }
+}
Code Review / simantics / platform.git / blobdiff