add partition list examples

guava/src/test/java/org/baeldung/java/CollectionJavaPartitionUnitTest.java

@@ -0,0 +1,74 @@
+package org.baeldung.java;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.junit.Assert.assertThat;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+import com.google.common.collect.Lists;
+
+public class CollectionJavaPartitionUnitTest {
+
+    // java8 groupBy
+    @Test
+    public final void givenList_whenParitioningIntoNSublistsUsingGroupingBy_thenCorrect() {
+        final List<Integer> intList = Lists.newArrayList(1, 2, 3, 4, 5, 6, 7, 8);
+
+        final Map<Integer, List<Integer>> groups = intList.stream().collect(Collectors.groupingBy(s -> (s - 1) / 3));
+        final List<List<Integer>> subSets = new ArrayList<List<Integer>>(groups.values());
+
+        // When
+        final List<Integer> lastPartition = subSets.get(2);
+        final List<Integer> expectedLastPartition = Lists.<Integer> newArrayList(7, 8);
+        assertThat(subSets.size(), equalTo(3));
+        assertThat(lastPartition, equalTo(expectedLastPartition));
+
+        // intList.add(9);
+        // System.out.println(groups.values());
+    }
+
+    // java8 partitionBy
+    @Test
+    public final void givenList_whenParitioningIntoSublistsUsingPartitionBy_thenCorrect() {
+        final List<Integer> intList = Lists.newArrayList(1, 2, 3, 4, 5, 6, 7, 8);
+
+        final Map<Boolean, List<Integer>> groups = intList.stream().collect(Collectors.partitioningBy(s -> s > 6));
+        final List<List<Integer>> subSets = new ArrayList<List<Integer>>(groups.values());
+
+        // When
+        final List<Integer> lastPartition = subSets.get(1);
+        final List<Integer> expectedLastPartition = Lists.<Integer> newArrayList(7, 8);
+        assertThat(subSets.size(), equalTo(2));
+        assertThat(lastPartition, equalTo(expectedLastPartition));
+
+        // intList.add(9);
+        // System.out.println(groups.values());
+    }
+
+    // java8 split by separator
+    @Test
+    public final void givenList_whenSplittingBySeparator_thenCorrect() {
+        final List<Integer> intList = Lists.newArrayList(1, 2, 3, 0, 4, 5, 6, 0, 7, 8);
+
+        final int[] indexes = Stream.of(IntStream.of(-1), IntStream.range(0, intList.size()).filter(i -> intList.get(i) == 0), IntStream.of(intList.size())).flatMapToInt(s -> s).toArray();
+        final List<List<Integer>> subSets = IntStream.range(0, indexes.length - 1).mapToObj(i -> intList.subList(indexes[i] + 1, indexes[i + 1])).collect(Collectors.toList());
+
+        // When
+        final List<Integer> lastPartition = subSets.get(2);
+        final List<Integer> expectedLastPartition = Lists.<Integer> newArrayList(7, 8);
+        assertThat(subSets.size(), equalTo(3));
+        assertThat(lastPartition, equalTo(expectedLastPartition));
+    }
+
+
+
+
+
+}