StreamIntermediateExample.java

package com.levelup.java.util.stream;

import static org.hamcrest.collection.IsIterableContainingInOrder.contains;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThat;

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import org.junit.Test;

/**
 * This java example will demonstrate stream
 * intermediate examples. 
 * 
 * @author Justin Musgrove
 * @see <a href='http://www.leveluplunch.com/java/examples/stream-intermediate-operations-example/'>Stream intermediate operations</a>
 */
public class StreamIntermediateExample {

	@Test
	public void intermediate_filter() {

		long elementsLessThanThree = Stream.of(1, 2, 3, 4)
				.filter(p -> p.intValue() < 3).count();

		assertEquals(2, elementsLessThanThree);
	}

	@Test
	public void intermediate_map() {

		List<String> strings = Stream.of("one", null, "three").map(s -> {
			if (s == null)
				return "[unknown]";
			else
				return s;
		}).collect(Collectors.toList());

		assertThat(strings, contains("one", "[unknown]", "three"));

	}

	@Test
	public void intermediate_flatmap() {

		// see CountWordOccurrencesInFile.java
	}
	

	@Test
	public void intermediate_peek() {

		List<String> strings = Stream.of("Badgers", "finals", "four")
				.filter(s -> s.length() >= 4).peek(s -> System.out.println(s))
				.map(s -> s.toUpperCase()).collect(Collectors.toList());

		assertThat(strings, contains("BADGERS", "FINALS", "FOUR"));
	}

	@Test
	public void intermediate_distinct() {

		List<Integer> distinctIntegers = IntStream.of(5, 6, 6, 6, 3, 2, 2)
				.distinct().boxed().collect(Collectors.toList());

		assertEquals(4, distinctIntegers.size());
		assertThat(distinctIntegers, contains(5, 6, 3, 2));

	}

	@Test
	public void intermediate_sorted() {

		List<Integer> sortedNumbers = Stream.of(5, 3, 1, 3, 6).sorted()
				.collect(Collectors.toList());

		assertThat(sortedNumbers, contains(1, 3, 3, 5, 6));
	}

	@Test
	public void intermediate_limit() {

		List<String> vals = Stream.of("limit", "by", "two").limit(2)
				.collect(Collectors.toList());

		assertThat(vals, contains("limit", "by"));
	}

}