StreamReduceTest.java

package streams;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.CoreMatchers.*;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.function.BinaryOperator;

import org.junit.Test;

public class StreamReduceTest {

	@Test
	public void shouldReduceTheListOfNumbers() throws Exception {
		List<Integer> numbers = Arrays.asList(1, 2, 5);
		
		Optional<Integer> reduced = numbers
			.stream()
			.reduce(new BinaryOperator<Integer>() {
				
				@Override
				public Integer apply(Integer first, Integer second) {
					return first + second;
				}
			});
		
		assertThat(reduced.isPresent(), is(true));
		assertThat(reduced.get(), equalTo(8));
	}
	
	@Test
	public void shouldReduceTheListOfNumbersByUsingLambdaExpression() throws Exception {
		List<Integer> numbers = Arrays.asList(1, 2, 5);
		
		Optional<Integer> reduced = numbers
				.stream()
				.reduce((first, second) -> first + second); 
		
		assertThat(reduced.isPresent(), is(true));
		assertThat(reduced.get(), equalTo(8));
	}
	
}