Code for the article "Java 8 Stream API Tutorial"

alexVengrovsk · alexVengrovsk · commit 9835081ad303 · 2016-06-10T23:12:04.000+03:00
alextrentton@gmail.com

Signed-off-by: &lt;alextrentton@gmail.com&gt;
diff --git a/core-java-8/src/main/java/com/baeldung/streamApi/Product.java b/core-java-8/src/main/java/com/baeldung/streamApi/Product.java
@@ -0,0 +1,51 @@
+package com.baeldung.streamApi;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+/**
+ * Created by Alex Vengr
+ */
+public class Product {
+
+    private int price;
+
+    private String name;
+
+    private boolean utilize;
+
+    public Product(int price, String name) {
+        this(price);
+        this.name = name;
+    }
+
+    public Product(int price) {
+        this.price = price;
+    }
+
+    public Product() {
+    }
+
+    public int getPrice() {
+        return price;
+    }
+
+    public void setPrice(int price) {
+        this.price = price;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+
+    public static Stream<String> streamOf(List<String> list) {
+        return (list == null || list.isEmpty()) ? Stream.empty() : list.stream();
+    }
+}
diff --git a/core-java-8/src/test/java/com/baeldung/java8/Java8StreamApiTest.java b/core-java-8/src/test/java/com/baeldung/java8/Java8StreamApiTest.java
@@ -0,0 +1,269 @@
+package com.baeldung.java8;
+
+import com.baeldung.streamApi.Product;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.*;
+import java.util.logging.Logger;
+import java.util.regex.Pattern;
+import java.util.stream.*;
+
+import static org.junit.Assert.*;
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Created by Alex Vengr
+ */
+public class Java8StreamApiTest {
+
+    private long counter;
+
+    private static Logger log = Logger.getAnonymousLogger();
+
+    private List<Product> productList;
+
+
+    @Before
+    public void init() {
+        productList = Arrays.asList(new Product(23, "potatoes"),
+          new Product(14, "orange"), new Product(13, "lemon"),
+            new Product(23, "bread"), new Product(13, "sugar"));
+    }
+
+    @Test
+    public void checkPipeline_whenStreamOneElementShorter_thenCorrect() {
+
+        List<String> list = Arrays.asList("abc1", "abc2", "abc3");
+        long size = list.stream().skip(1)
+          .map(element -> element.substring(0, 3)).count();
+        assertEquals(list.size() - 1, size);
+    }
+
+    @Test
+    public void checkOrder_whenChangeQuantityOfMethodCalls_thenCorrect() {
+
+        List<String> list = Arrays.asList("abc1", "abc2", "abc3");
+
+        counter = 0;
+        long sizeFirst = list.stream()
+          .skip(2).map(element -> {
+              wasCalled();
+              return element.substring(0, 3);
+          }).count();
+        assertEquals( 1, counter);
+
+        counter = 0;
+        long sizeSecond = list.stream().map(element -> {
+            wasCalled();
+            return element.substring(0, 3);
+        }).skip(2).count();
+        assertEquals( 3, counter);
+    }
+
+    @Test
+    public void createEmptyStream_whenEmpty_thenCorrect() {
+
+        Stream<String> streamEmpty = Stream.empty();
+        assertEquals(0, streamEmpty.count());
+
+        List<String> names = Collections.emptyList();
+        Stream<String> streamOf = Product.streamOf(names);
+        assertTrue(streamOf.count() == 0);
+    }
+
+    @Test
+    public void createStream_whenCreated_thenCorrect() {
+
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> streamOfCollection = collection.stream();
+        assertEquals(3, streamOfCollection.count());
+
+        Stream<String> streamOfArray = Stream.of("a", "b", "c");
+        assertEquals(3, streamOfArray.count());
+
+        String[] arr = new String[]{"a", "b", "c"};
+        Stream<String> streamOfArrayPart = Arrays.stream(arr, 1, 3);
+        assertEquals(2, streamOfArrayPart.count());
+
+        IntStream intStream = IntStream.range(1, 3);
+        LongStream longStream = LongStream.rangeClosed(1, 3);
+        Random random = new Random();
+        DoubleStream doubleStream = random.doubles(3);
+        assertEquals(2, intStream.count());
+        assertEquals(3, longStream.count());
+        assertEquals(3, doubleStream.count());
+
+        IntStream streamOfChars = "abc".chars();
+        IntStream str = "".chars();
+        assertEquals(3, streamOfChars.count());
+
+        Stream<String> streamOfString = Pattern.compile(", ").splitAsStream("a, b, c");
+        assertEquals("a", streamOfString.findFirst().get());
+
+        Path path = getPath();
+        Stream<String> streamOfStrings = null;
+        try {
+            streamOfStrings = Files.lines(path, Charset.forName("UTF-8"));
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        assertEquals("a", streamOfStrings.findFirst().get());
+
+        Stream<String> streamBuilder = Stream.<String>builder().add("a").add("b").add("c").build();
+        assertEquals(3, streamBuilder.count());
+
+        Stream<String> streamGenerated = Stream.generate(() -> "element").limit(10);
+        assertEquals(10, streamGenerated.count());
+
+        Stream<Integer> streamIterated = Stream.iterate(40, n -> n + 2).limit(20);
+        assertTrue(40 <= streamIterated.findAny().get());
+    }
+
+    @Test
+    public void runStreamPipeline_whenOrderIsRight_thenCorrect() {
+
+        List<String> list = Arrays.asList("abc1", "abc2", "abc3");
+        Optional<String> stream = list.stream()
+          .filter(element -> {
+              log.info("filter() was called");
+              return element.contains("2");
+          }).map(element -> {
+              log.info("map() was called");
+              return element.toUpperCase();
+          }).findFirst();
+    }
+
+    @Test
+    public void reduce_whenExpected_thenCorrect() {
+
+        OptionalInt reduced = IntStream.range(1, 4).reduce((a, b) -> a + b);
+        assertEquals(6, reduced.getAsInt());
+
+        int reducedTwoParams = IntStream.range(1, 4).reduce(10, (a, b) -> a + b);
+        assertEquals(16, reducedTwoParams);
+
+        int reducedThreeParams = Stream.of(1, 2, 3)
+          .reduce(10, (a, b) -> a + b, (a, b) -> {
+              log.info("combiner was called");
+              return a + b;
+          });
+        assertEquals(16, reducedThreeParams);
+
+        int reducedThreeParamsParallel = Arrays.asList(1, 2, 3).parallelStream()
+          .reduce(10, (a, b) -> a + b, (a, b) -> {
+              log.info("combiner was called");
+              return a + b;
+          });
+        assertEquals(36, reducedThreeParamsParallel);
+    }
+
+    @Test
+    public void collecting_whenAsExpected_thenCorrect() {
+
+        List<String> collectorCollection = productList.stream()
+          .map(Product::getName).collect(Collectors.toList());
+
+        assertTrue(collectorCollection instanceof List);
+        assertEquals(5, collectorCollection.size());
+
+        String listToString = productList.stream().map(Product::getName)
+          .collect(Collectors.joining(", ", "[", "]"));
+
+        assertTrue(listToString.contains(",") && listToString.contains("[") && listToString.contains("]"));
+
+        double averagePrice = productList.stream().collect(Collectors.averagingInt(Product::getPrice));
+        assertTrue(17.2 == averagePrice);
+
+        int summingPrice = productList.stream().collect(Collectors.summingInt(Product::getPrice));
+        assertEquals(86, summingPrice);
+
+        IntSummaryStatistics statistics = productList.stream()
+          .collect(Collectors.summarizingInt(Product::getPrice));
+        assertEquals(23, statistics.getMax());
+
+        Map<Integer, List<Product>> collectorMapOfLists = productList.stream()
+          .collect(Collectors.groupingBy(Product::getPrice));
+        assertEquals(3, collectorMapOfLists.keySet().size());
+
+        Map<Boolean, List<Product>> mapPartioned = productList.stream()
+          .collect(Collectors.partitioningBy(element -> element.getPrice() > 15));
+        assertEquals(2, mapPartioned.keySet().size());
+
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void collect_whenThrows_thenCorrect() {
+        Set<Product> unmodifiableSet = productList.stream()
+          .collect(Collectors.collectingAndThen(Collectors.toSet(),
+            Collections::unmodifiableSet));
+        unmodifiableSet.add(new Product(4, "tea"));
+    }
+
+    @Test
+    public void customCollector_whenResultContainsAllElementsFrSource_thenCorrect() {
+        Collector<Product, ?, LinkedList<Product>> toLinkedList =
+          Collector.of(LinkedList::new, LinkedList::add,
+            (first, second) -> { first.addAll(second); return first; });
+
+        LinkedList<Product> linkedListOfPersons = productList.stream().collect(toLinkedList);
+        assertTrue(linkedListOfPersons.containsAll(productList));
+    }
+
+    @Test
+    public void parallelStream_whenWorks_thenCorrect() {
+        Stream<Product> streamOfCollection = productList.parallelStream();
+        boolean isParallel = streamOfCollection.isParallel();
+        boolean haveBigPrice = streamOfCollection.map(product -> product.getPrice() * 12)
+          .anyMatch(price -> price > 200);
+        assertTrue(isParallel && haveBigPrice);
+    }
+
+    @Test
+    public void parallel_whenIsParallel_thenCorrect() {
+        IntStream intStreamParallel =
+          IntStream.range(1, 150).parallel().map(element -> element * 34);
+        boolean isParallel = intStreamParallel.isParallel();
+        assertTrue(isParallel);
+    }
+
+    @Test
+    public void parallel_whenIsSequential_thenCorrect() {
+        IntStream intStreamParallel =
+          IntStream.range(1, 150).parallel().map(element -> element * 34);
+        IntStream intStreamSequential = intStreamParallel.sequential();
+        boolean isParallel = intStreamParallel.isParallel();
+        assertFalse(isParallel);
+    }
+
+    private Path getPath() {
+        Path path = null;
+        try {
+            path = Files.createTempFile(null, ".txt");
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        try (BufferedWriter writer = Files.newBufferedWriter(path)) {
+            writer.write("a\nb\nc");
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return path;
+    }
+
+    private void wasCalled() {
+        counter++;
+    }
+}
