1berry/openjdk
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

8019401: Collectors.collectingAndThen

Browse Source 
Reviewed-by: mduigou
This commit is contained in:
Brian Goetz 2013-08-12 12:06:50 -04:00 committed by Brian Goetz
parent d2956c2e8d
commit 4030ed819b
2 changed files with 52 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
jdk/src/share/classes/java/util/stream/Collectors.java
View File

@ -353,6 +353,43 @@ public final class Collectors {
downstream.characteristics());
}
/**
* Adapts a {@code Collector} to perform an additional finishing
* transformation. For example, one could adapt the {@link #toList()}
* collector to always produce an immutable list with:
* <pre>{@code
* List<String> people
* = people.stream().collect(collectingAndThen(toList(), Collections::unmodifiableList));
* }</pre>
*
* @param <T> the type of the input elements
* @param <A> intermediate accumulation type of the downstream collector
* @param <R> result type of the downstream collector
* @param <RR> result type of the resulting collector
* @param downstream a collector
* @param finisher a function to be applied to the final result of the downstream collector
* @return a collector which performs the action of the downstream collector,
* followed by an additional finishing step
*/
public static<T,A,R,RR> Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream,
Function<R,RR> finisher) {
Set<Collector.Characteristics> characteristics = downstream.characteristics();
if (characteristics.contains(Collector.Characteristics.IDENTITY_FINISH)) {
if (characteristics.size() == 1)
characteristics = Collectors.CH_NOID;
else {
characteristics = EnumSet.copyOf(characteristics);
characteristics.remove(Collector.Characteristics.IDENTITY_FINISH);
characteristics = Collections.unmodifiableSet(characteristics);
}
}
return new CollectorImpl<>(downstream.supplier(),
downstream.accumulator(),
downstream.combiner(),
downstream.finisher().andThen(finisher),
characteristics);
}
/**
* Returns a {@code Collector} accepting elements of type {@code T} that
* counts the number of input elements. If no elements are present, the

15
jdk/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java
View File

@ -25,6 +25,7 @@ package org.openjdk.tests.java.util.stream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
@ -52,6 +53,7 @@ import java.util.stream.TestData;
import org.testng.annotations.Test;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.groupingByConcurrent;
import static java.util.stream.Collectors.partitioningBy;
@ -603,4 +605,17 @@ public class TabulatorsTest extends OpTestCase {
new PartitionAssertion<>(classifier,
new ReduceAssertion<>(0, LambdaTestHelpers.identity(), Integer::sum)));
}
@Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
public void testComposeFinisher(String name, TestData.OfRef<Integer> data) throws ReflectiveOperationException {
List<Integer> asList = exerciseTerminalOps(data, s -> s.collect(toList()));
List<Integer> asImmutableList = exerciseTerminalOps(data, s -> s.collect(collectingAndThen(toList(), Collections::unmodifiableList)));
assertEquals(asList, asImmutableList);
try {
asImmutableList.add(0);
fail("Expecting immutable result");
}
catch (UnsupportedOperationException ignored) { }
}
}