Merge pull request #871 from tochoromero/master

BAEL-7: Join and Split Collections

core-java/src/test/java/org/baeldung/java/collections/JoinSplitCollectionsUnitTest.java

@@ -0,0 +1,179 @@
+package org.baeldung.java.collections;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+public class JoinSplitCollectionsUnitTest {
+
+	@Test
+	public void whenJoiningTwoArrays_thenJoined() {
+		String[] animals1 = new String[] { "Dog", "Cat" };
+		String[] animals2 = new String[] { "Bird", "Cow" };
+		String[] result = Stream.concat(Arrays.stream(animals1), Arrays.stream(animals2))
+				.toArray(String[]::new);
+
+		assertArrayEquals(result, new String[] { "Dog", "Cat", "Bird", "Cow" });
+	}
+	
+	@Test
+	public void whenJoiningTwoCollections_thenJoined() {
+		Collection<Integer> collection1 = Arrays.asList(7, 8, 9);
+		Collection<Integer> collection2 = Arrays.asList(10, 11, 12);
+		Collection<Integer> result = Stream.concat(collection1.stream(), collection2.stream())
+				.collect(Collectors.toList());
+	
+		assertTrue(result.equals(Arrays.asList(7, 8, 9, 10, 11, 12)));
+	}
+
+	@Test
+	public void whenJoiningTwoCollectionsWithFilter_thenJoined() {
+		Collection<Integer> collection1 = Arrays.asList(7, 8, 11);
+		Collection<Integer> collection2 = Arrays.asList(9, 12, 10);
+		Collection<Integer> result = Stream.concat(collection1.stream(), collection2.stream())
+				.filter(next -> next <= 10)
+				.collect(Collectors.toList());
+	
+		assertTrue(result.equals(Arrays.asList(7, 8, 9, 10)));
+	}
+
+	@Test
+	public void whenConvertArrayToString_thenConverted() {
+		String[] colors = new String[] { "Red", "Blue", "Green", "Yellow" };
+		String result = Arrays.stream(colors)
+				.collect(Collectors.joining(", "));
+
+		assertEquals(result, "Red, Blue, Green, Yellow");
+	}
+
+	@Test
+	public void whenConvertCollectionToString_thenConverted() {
+		Collection<String> directions = Arrays.asList("Left", "Right", "Top", "Bottom");
+		String result = directions.stream()
+				.collect(Collectors.joining(", "));
+	
+		assertEquals(result, "Left, Right, Top, Bottom");
+	}
+
+	@Test
+	public void whenConvertMapToString_thenConverted() {
+		Map<Integer, String> users = new HashMap<>();
+		users.put(1, "John Doe");
+		users.put(2, "Paul Smith");
+		users.put(3, "Susan Anderson");
+
+		String result = users.entrySet().stream().map(entry -> entry.getKey() + " = " + entry.getValue())
+				.collect(Collectors.joining(", "));
+
+		assertEquals(result, "1 = John Doe, 2 = Paul Smith, 3 = Susan Anderson");
+	}
+
+	@Test
+	public void whenConvertNestedCollectionToString_thenConverted() {
+		Collection<List<String>> nested = new ArrayList<>();
+		nested.add(Arrays.asList("Left", "Right", "Top", "Bottom"));
+		nested.add(Arrays.asList("Red", "Blue", "Green", "Yellow"));
+	
+		String result = nested.stream()
+				.map(nextList -> nextList.stream()
+						.collect(Collectors.joining("-")))
+				.collect(Collectors.joining("; "));
+	
+		assertEquals(result, "Left-Right-Top-Bottom; Red-Blue-Green-Yellow");
+	}
+
+	@Test
+	public void whenConvertCollectionToStringAndSkipNull_thenConverted() {
+		Collection<String> fruits = Arrays.asList("Apple", "Orange", null, "Grape");
+		String result = fruits.stream()
+				.filter(next -> next != null)
+				.collect(Collectors.joining(", "));
+	
+		assertEquals(result, "Apple, Orange, Grape");
+	}
+
+	@Test
+	public void whenSplitCollectionHalf_thenConverted() {
+		Collection<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+		Collection<Integer> result1 = new ArrayList<>();
+		Collection<Integer> result2 = new ArrayList<>();
+		AtomicInteger count = new AtomicInteger();
+		int midpoint = Math.round(numbers.size() / 2);
+		
+		numbers.forEach(next -> {
+			int index = count.getAndIncrement();
+			if(index < midpoint){
+				result1.add(next);
+			}else{
+				result2.add(next);
+			}
+		});
+		
+		assertTrue(result1.equals(Arrays.asList(1, 2, 3, 4, 5)));
+		assertTrue(result2.equals(Arrays.asList(6, 7, 8, 9, 10)));
+	}
+	
+	@Test
+	public void whenSplitArrayByWordLength_thenConverted() {
+		String[] words = new String[]{"bye", "cold", "it", "and", "my", "word"};
+		Map<Integer, List<String>> result = Arrays.stream(words)
+				.collect(Collectors.groupingBy(word -> word.length()));
+		
+		assertTrue(result.get(2).equals(Arrays.asList("it", "my")));
+		assertTrue(result.get(3).equals(Arrays.asList("bye", "and")));
+		assertTrue(result.get(4).equals(Arrays.asList("cold", "word")));
+	}
+
+	@Test
+	public void whenConvertStringToArray_thenConverted() {
+		String colors = "Red, Blue, Green, Yellow";
+		String[] result = colors.split(", ");
+
+		assertArrayEquals(result, new String[] { "Red", "Blue", "Green", "Yellow" });
+	}
+
+	@Test
+	public void whenConvertStringToCollection_thenConverted() {
+		String colors = "Left, Right, Top, Bottom";
+		Collection<String> result = Arrays.asList(colors.split(", "));
+
+		assertTrue(result.equals(Arrays.asList("Left", "Right", "Top", "Bottom")));
+	}
+
+	@Test
+	public void whenConvertStringToMap_thenConverted() {
+		String users = "1 = John Doe, 2 = Paul Smith, 3 = Susan Anderson";
+
+		Map<Integer, String> result = Arrays.stream(users.split(", "))
+				.map(next -> next.split(" = "))
+				.collect(Collectors.toMap(entry -> Integer.parseInt(entry[0]), entry -> entry[1]));
+
+		assertEquals(result.get(1), "John Doe");
+		assertEquals(result.get(2), "Paul Smith");
+		assertEquals(result.get(3), "Susan Anderson");
+	}
+
+	@Test
+	public void whenConvertCollectionToStringMultipleSeparators_thenConverted() {
+		String fruits = "Apple. , Orange, Grape. Lemon";
+
+		Collection<String> result = Arrays.stream(fruits.split("[,|.]"))
+				.map(String::trim)
+				.filter(next -> !next.isEmpty())
+				.collect(Collectors.toList());
+
+		assertTrue(result.equals(Arrays.asList("Apple", "Orange", "Grape", "Lemon")));
+	}
+}