FlatMapTest.java

package com.annimon.stream.longstreamtests;

import com.annimon.stream.LongStream;
import com.annimon.stream.function.LongFunction;
import java.util.NoSuchElementException;
import org.junit.Test;
import static com.annimon.stream.test.hamcrest.LongStreamMatcher.assertElements;
import static org.hamcrest.Matchers.arrayContaining;

public final class FlatMapTest {

    @Test
    public void testFlatMap() {
        LongFunction<LongStream> twicer = new LongFunction<LongStream>() {
            @Override
            public LongStream apply(long value) {
                return LongStream.of(value, value);
            }
        };
        LongStream.of(10L, 20L, 30L)
                .flatMap(twicer)
                .custom(assertElements(arrayContaining(
                        10L, 10L,
                        20L, 20L,
                        30L, 30L
                )));

        LongStream.of(10L, 20L, -30L)
                .flatMap(new LongFunction<LongStream>() {
                    @Override
                    public LongStream apply(long value) {
                        if (value < 0) return LongStream.of(value);
                        return null;
                    }
                })
                .custom(assertElements(arrayContaining(
                        -30L
                )));

        LongStream.of(10L, 20L, -30L)
                .flatMap(new LongFunction<LongStream>() {
                    @Override
                    public LongStream apply(long value) {
                        if (value < 0) return LongStream.empty();
                        return LongStream.of(value);
                    }
                })
                .custom(assertElements(arrayContaining(
                        10L, 20L
                )));
    }

    @Test(expected = NoSuchElementException.class)
    public void testFlatMapIterator() {
        LongStream.empty().flatMap(new LongFunction<LongStream>() {
            @Override
            public LongStream apply(long value) {
                return LongStream.of(value);
            }
        }).iterator().nextLong();
    }
}