ReduceTest.java

package com.annimon.stream.streamtests;

import com.annimon.stream.Functions;
import com.annimon.stream.Optional;
import com.annimon.stream.Stream;
import com.annimon.stream.function.BiFunction;
import org.junit.Test;
import static com.annimon.stream.test.hamcrest.OptionalMatcher.isEmpty;
import static com.annimon.stream.test.hamcrest.OptionalMatcher.isPresent;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertThat;

public final class ReduceTest {

    @Test
    public void testReduceSumFromZero() {
        int result = Stream.range(0, 10)
                .reduce(0, Functions.addition());
        assertEquals(45, result);
    }

    @Test
    public void testReduceSumFromMinus45() {
        int result = Stream.range(0, 10)
                .reduce(-45, Functions.addition());
        assertEquals(0, result);
    }

    @Test
    public void testReduceWithAnotherType() {
        int result = Stream.of("a", "bb", "ccc", "dddd")
                .reduce(0, new BiFunction<Integer, String, Integer>() {
                    @Override
                    public Integer apply(Integer length, String s) {
                        return length + s.length();
                    }
                });
        assertEquals(10, result);
    }

    @Test
    public void testReduceOptional() {
        Optional<Integer> result = Stream.range(0, 10)
                .reduce(Functions.addition());

        assertThat(result, isPresent());
        assertNotNull(result.get());
        assertEquals(45, (int) result.get());
    }
    
    @Test
    public void testReduceOptionalOnEmptyStream() {
        Optional<Integer> result = Stream.<Integer>empty()
                .reduce(Functions.addition());

        assertThat(result, isEmpty());
        assertEquals(119, (int) result.orElse(119));
    }
}