8015317: Optional.filter, map, and flatMap
Reviewed-by: psandoz, mduigou
Contributed-by: brian.goetz@oracle.com, henry.jen@oracle.com
--- a/jdk/src/share/classes/java/util/Optional.java Fri Jul 12 11:11:30 2013 -0700
+++ b/jdk/src/share/classes/java/util/Optional.java Fri Jul 12 11:12:16 2013 -0700
@@ -25,6 +25,8 @@
package java.util;
import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Predicate;
import java.util.function.Supplier;
/**
@@ -52,7 +54,7 @@
private final T value;
/**
- * Construct an empty instance.
+ * Constructs an empty instance.
*
* @implNote Generally only one empty instance, {@link Optional#EMPTY},
* should exist per VM.
@@ -80,7 +82,7 @@
}
/**
- * Construct an instance with the value present.
+ * Constructs an instance with the value present.
*
* @param value the non-null value to be present
*/
@@ -89,7 +91,7 @@
}
/**
- * Return an {@code Optional} with the specified present value.
+ * Returns an {@code Optional} with the specified present non-null value.
*
* @param value the value to be present, which must be non-null
* @return an {@code Optional} with the value present
@@ -99,6 +101,18 @@
}
/**
+ * Returns an {@code Optional} describing the specified value, if non-null,
+ * otherwise returns an empty {@code Optional}.
+ *
+ * @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> Optional<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}.
*
@@ -124,7 +138,7 @@
}
/**
- * Have the specified consumer accept the value if a value is present,
+ * 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
@@ -137,6 +151,89 @@
}
/**
+ * 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 NullPointerException if the predicate is null
+ */
+ public Optional<T> filter(Predicate<? super T> predicate) {
+ 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 NullPointerException if the mapping function is null
+ */
+ public<U> Optional<U> map(Function<? super T, ? extends U> mapper) {
+ Objects.requireNonNull(mapper);
+ if (!isPresent())
+ return empty();
+ else {
+ return Optional.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 NullPointerException if the mapping function is null or returns
+ * a null result
+ */
+ public<U> Optional<U> flatMap(Function<? super T, Optional<U>> mapper) {
+ 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
--- a/jdk/src/share/classes/java/util/OptionalDouble.java Fri Jul 12 11:11:30 2013 -0700
+++ b/jdk/src/share/classes/java/util/OptionalDouble.java Fri Jul 12 11:12:16 2013 -0700
@@ -186,10 +186,10 @@
}
/**
- * Indicates whether some other object is "equal to" this Optional. The
+ * Indicates whether some other object is "equal to" this OptionalDouble. The
* other object is considered equal if:
* <ul>
- * <li>it is also an {@code OptionalInt} and;
+ * <li>it is also an {@code OptionalDouble} and;
* <li>both instances have no value present or;
* <li>the present values are "equal to" each other via {@code Double.compare() == 0}.
* </ul>
@@ -226,12 +226,14 @@
}
/**
- * Returns a non-empty string representation of this OptionalDouble suitable for
+ * {@inheritDoc}
+ *
+ * Returns a non-empty string representation of this object 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 OptionalDoubless must be
+ * representation in the result. Empty and present instances must be
* unambiguously differentiable.
*
* @return the string representation of this instance
--- a/jdk/src/share/classes/java/util/OptionalInt.java Fri Jul 12 11:11:30 2013 -0700
+++ b/jdk/src/share/classes/java/util/OptionalInt.java Fri Jul 12 11:12:16 2013 -0700
@@ -186,7 +186,7 @@
}
/**
- * Indicates whether some other object is "equal to" this Optional. The
+ * Indicates whether some other object is "equal to" this OptionalInt. The
* other object is considered equal if:
* <ul>
* <li>it is also an {@code OptionalInt} and;
@@ -226,12 +226,14 @@
}
/**
- * Returns a non-empty string representation of this OptionalInt suitable for
+ * {@inheritDoc}
+ *
+ * Returns a non-empty string representation of this object 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 OptionalInts must be
+ * representation in the result. Empty and present instances must be
* unambiguously differentiable.
*
* @return the string representation of this instance
--- a/jdk/src/share/classes/java/util/OptionalLong.java Fri Jul 12 11:11:30 2013 -0700
+++ b/jdk/src/share/classes/java/util/OptionalLong.java Fri Jul 12 11:12:16 2013 -0700
@@ -186,10 +186,10 @@
}
/**
- * Indicates whether some other object is "equal to" this Optional. The
+ * Indicates whether some other object is "equal to" this OptionalLong. The
* other object is considered equal if:
* <ul>
- * <li>it is also an {@code OptionalInt} and;
+ * <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>
@@ -226,12 +226,14 @@
}
/**
- * Returns a non-empty string representation of this OptionalLong suitable for
+ * {@inheritDoc}
+ *
+ * Returns a non-empty string representation of this object 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 OptionalLongs must be
+ * representation in the result. Empty and present instances must be
* unambiguously differentiable.
*
* @return the string representation of this instance
--- a/jdk/test/java/util/Optional/Basic.java Fri Jul 12 11:11:30 2013 -0700
+++ b/jdk/test/java/util/Optional/Basic.java Fri Jul 12 11:12:16 2013 -0700
@@ -58,36 +58,36 @@
assertSame(Boolean.FALSE, empty.orElseGet(()-> Boolean.FALSE));
}
- @Test(expectedExceptions=NoSuchElementException.class)
- public void testEmptyGet() {
- Optional<Boolean> empty = Optional.empty();
+ @Test(expectedExceptions=NoSuchElementException.class)
+ public void testEmptyGet() {
+ Optional<Boolean> empty = Optional.empty();
- Boolean got = empty.get();
- }
+ Boolean got = empty.get();
+ }
- @Test(expectedExceptions=NullPointerException.class)
- public void testEmptyOrElseGetNull() {
- Optional<Boolean> empty = Optional.empty();
+ @Test(expectedExceptions=NullPointerException.class)
+ public void testEmptyOrElseGetNull() {
+ Optional<Boolean> empty = Optional.empty();
- Boolean got = empty.orElseGet(null);
- }
+ Boolean got = empty.orElseGet(null);
+ }
- @Test(expectedExceptions=NullPointerException.class)
- public void testEmptyOrElseThrowNull() throws Throwable {
- Optional<Boolean> empty = Optional.empty();
+ @Test(expectedExceptions=NullPointerException.class)
+ public void testEmptyOrElseThrowNull() throws Throwable {
+ Optional<Boolean> empty = Optional.empty();
- Boolean got = empty.orElseThrow(null);
- }
+ Boolean got = empty.orElseThrow(null);
+ }
- @Test(expectedExceptions=ObscureException.class)
- public void testEmptyOrElseThrow() throws Exception {
- Optional<Boolean> empty = Optional.empty();
+ @Test(expectedExceptions=ObscureException.class)
+ public void testEmptyOrElseThrow() throws Exception {
+ Optional<Boolean> empty = Optional.empty();
- Boolean got = empty.orElseThrow(ObscureException::new);
- }
+ Boolean got = empty.orElseThrow(ObscureException::new);
+ }
- @Test(groups = "unit")
- public void testPresent() {
+ @Test(groups = "unit")
+ public void testPresent() {
Optional<Boolean> empty = Optional.empty();
Optional<String> presentEmptyString = Optional.of("");
Optional<Boolean> present = Optional.of(Boolean.TRUE);
@@ -116,6 +116,116 @@
assertSame(Boolean.TRUE, present.<RuntimeException>orElseThrow(ObscureException::new));
}
+ @Test(groups = "unit")
+ public void testOfNullable() {
+ Optional<String> instance = Optional.ofNullable(null);
+ assertFalse(instance.isPresent());
+
+ instance = Optional.ofNullable("Duke");
+ assertTrue(instance.isPresent());
+ assertEquals(instance.get(), "Duke");
+ }
+
+ @Test(groups = "unit")
+ public void testFilter() {
+ // Null mapper function
+ Optional<String> empty = Optional.empty();
+ Optional<String> duke = Optional.of("Duke");
+
+ try {
+ Optional<String> result = empty.filter(null);
+ fail("Should throw NPE on null mapping function");
+ } catch (NullPointerException npe) {
+ // expected
+ }
+
+ Optional<String> result = empty.filter(String::isEmpty);
+ assertFalse(result.isPresent());
+
+ result = duke.filter(String::isEmpty);
+ assertFalse(result.isPresent());
+ result = duke.filter(s -> s.startsWith("D"));
+ assertTrue(result.isPresent());
+ assertEquals(result.get(), "Duke");
+
+ Optional<String> emptyString = Optional.of("");
+ result = emptyString.filter(String::isEmpty);
+ assertTrue(result.isPresent());
+ assertEquals(result.get(), "");
+ }
+
+ @Test(groups = "unit")
+ public void testMap() {
+ Optional<String> empty = Optional.empty();
+ Optional<String> duke = Optional.of("Duke");
+
+ // Null mapper function
+ try {
+ Optional<Boolean> b = empty.map(null);
+ fail("Should throw NPE on null mapping function");
+ } catch (NullPointerException npe) {
+ // expected
+ }
+
+ // Map an empty value
+ Optional<Boolean> b = empty.map(String::isEmpty);
+ assertFalse(b.isPresent());
+
+ // Map into null
+ b = empty.map(n -> null);
+ assertFalse(b.isPresent());
+ b = duke.map(s -> null);
+ assertFalse(b.isPresent());
+
+ // Map to value
+ Optional<Integer> l = duke.map(String::length);
+ assertEquals(l.get().intValue(), 4);
+ }
+
+ @Test(groups = "unit")
+ public void testFlatMap() {
+ Optional<String> empty = Optional.empty();
+ Optional<String> duke = Optional.of("Duke");
+
+ // Null mapper function
+ try {
+ Optional<Boolean> b = empty.flatMap(null);
+ fail("Should throw NPE on null mapping function");
+ } catch (NullPointerException npe) {
+ // expected
+ }
+
+ // Map into null
+ try {
+ Optional<Boolean> b = duke.flatMap(s -> null);
+ fail("Should throw NPE when mapper return null");
+ } catch (NullPointerException npe) {
+ // expected
+ }
+
+ // Empty won't invoke mapper function
+ try {
+ Optional<Boolean> b = empty.flatMap(s -> null);
+ assertFalse(b.isPresent());
+ } catch (NullPointerException npe) {
+ fail("Mapper function should not be invoked");
+ }
+
+ // Map an empty value
+ Optional<Integer> l = empty.flatMap(s -> Optional.of(s.length()));
+ assertFalse(l.isPresent());
+
+ // Map to value
+ Optional<Integer> fixture = Optional.of(Integer.MAX_VALUE);
+ l = duke.flatMap(s -> Optional.of(s.length()));
+ assertTrue(l.isPresent());
+ assertEquals(l.get().intValue(), 4);
+
+ // Verify same instance
+ l = duke.flatMap(s -> fixture);
+ assertSame(l, fixture);
+ }
+
private static class ObscureException extends RuntimeException {
}