* added examples of filtering collections using Streams, Apache CollectionUtils, Guava and Eclipse Collections

core-java-collections/pom.xml

@@ -36,15 +36,32 @@
             <artifactId>commons-lang3</artifactId>
             <version>${commons-lang3.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections-api</artifactId>
+            <version>9.2.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections</artifactId>
+            <version>9.2.0</version>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <properties>
+        <junit.platform.version>1.2.0</junit.platform.version>
         <commons-lang3.version>3.5</commons-lang3.version>
         <commons-collections4.version>4.1</commons-collections4.version>
         <collections-generic.version>4.01</collections-generic.version>

core-java-collections/src/main/java/com/baeldung/java/filtering/CollectionUtilsCollectionFilter.java

@@ -0,0 +1,22 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.collections4.Predicate;
+
+public class CollectionUtilsCollectionFilter {
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> apacheEventNumberPredicate = new Predicate<Integer>() {
+
+            @Override
+            public boolean evaluate(Integer object) {
+                return object % 2 == 0;
+            }
+        };
+
+        CollectionUtils.filter(baseCollection, apacheEventNumberPredicate);
+        return baseCollection;
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/filtering/EclipseCollectionsCollectionFilter.java

@@ -0,0 +1,32 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+
+import org.eclipse.collections.api.block.predicate.Predicate;
+import org.eclipse.collections.impl.factory.Lists;
+import org.eclipse.collections.impl.utility.Iterate;
+
+public class EclipseCollectionsCollectionFilter {
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> eclipsePredicate = item -> item % 2 == 0;
+        Collection<Integer> filteredList = Lists.mutable.ofAll(baseCollection)
+            .select(eclipsePredicate);
+
+        return filteredList;
+    }
+
+    static public Collection<Integer> findEvenNumbersUsingIterate(Collection<Integer> baseCollection) {
+        Predicate<Integer> eclipsePredicate = new Predicate<Integer>() {
+            private static final long serialVersionUID = 1L;
+
+            @Override
+            public boolean accept(Integer arg0) {
+                return arg0 % 2 == 0;
+            }
+        };
+        Collection<Integer> filteredList = Iterate.select(baseCollection, eclipsePredicate);
+
+        return filteredList;
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/filtering/GuavaCollectionFilter.java

@@ -0,0 +1,22 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+
+import com.google.common.base.Predicate;
+import com.google.common.collect.Collections2;
+
+public class GuavaCollectionFilter {
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> guavaPredicate = new Predicate<Integer>() {
+
+            @Override
+            public boolean apply(Integer input) {
+                return input % 2 == 0;
+            }
+        };
+        Collection<Integer> filteredCollection = Collections2.filter(baseCollection, guavaPredicate);
+        return filteredCollection;
+    }
+
+}

core-java-collections/src/main/java/com/baeldung/java/filtering/StreamsCollectionFilter.java

@@ -0,0 +1,37 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class StreamsCollectionFilter {
+
+    public static <T> Collection<T> filterCollectionHelperMethod(Collection<T> baseCollection, Predicate<T> predicate) {
+        return baseCollection.stream()
+            .filter(predicate)
+            .collect(Collectors.toList());
+    }
+
+    static public Collection<Integer> findEvenNumbersUsingHelperMethod(Collection<Integer> baseCollection) {
+        return filterCollectionHelperMethod(baseCollection, item -> item % 2 == 0);
+    }
+
+    static public Collection<Integer> findEvenNumbersUsingLambda(Collection<Integer> baseCollection) {
+        return baseCollection.stream()
+            .filter(item -> item % 2 == 0)
+            .collect(Collectors.toList());
+    }
+
+    static public Collection<Integer> findEvenNumbersUsingPredicate(Collection<Integer> baseCollection) {
+        Predicate<Integer> evenNumberPredicate = new Predicate<Integer>() {
+            @Override
+            public boolean test(Integer i) {
+                return i % 2 == 0;
+            }
+        };
+
+        return baseCollection.stream()
+            .filter(evenNumberPredicate)
+            .collect(Collectors.toList());
+    }
+}

core-java-collections/src/test/java/com/baeldung/java/filtering/CollectionFiltersUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.java.filtering;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+
+import org.junit.jupiter.api.Test;
+import org.junit.platform.runner.JUnitPlatform;
+import org.junit.runner.RunWith;
+
+@RunWith(JUnitPlatform.class)
+public class CollectionFiltersUnitTest {
+
+    private static final Collection<Integer> BASE_INTEGER_COLLECTION = Arrays.asList(9, 14, 2, 7, 1, 5, 8);
+    private static final Collection<Integer> EXPECTED_EVEN_FILTERED_COLLECTION = Arrays.asList(14, 2, 8);
+
+    @Test
+    public void givenAStringCollection_whenFilteringFourLetterWords_thenObtainTheFilteredCollection() {
+        final Collection<String> baseStrings = Arrays.asList("java", "baeldung", "type", "example", "other");
+
+        Collection<String> filtered = StreamsCollectionFilter.filterCollectionHelperMethod(baseStrings, item -> item.length() == 4);
+
+        assertThat(filtered).containsExactlyInAnyOrder("java", "type");
+    }
+
+    @Test
+    public void givenAnIntegerCollection_whenFilteringEvenValues_thenObtainTheFilteredCollectionForAllCases() {
+        Collection<Integer> filteredWithStreams1 = StreamsCollectionFilter.findEvenNumbersUsingLambda(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithStreams2 = StreamsCollectionFilter.findEvenNumbersUsingPredicate(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithCollectionUtils = CollectionUtilsCollectionFilter.findEvenNumbers(new ArrayList<>(BASE_INTEGER_COLLECTION));
+        Collection<Integer> filteredWithEclipseCollections = EclipseCollectionsCollectionFilter.findEvenNumbers(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithEclipseCollectionsUsingIterate = EclipseCollectionsCollectionFilter.findEvenNumbersUsingIterate(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithGuava = GuavaCollectionFilter.findEvenNumbers(BASE_INTEGER_COLLECTION);
+
+        assertThat(filteredWithStreams1).hasSameElementsAs(filteredWithStreams2)
+            .hasSameElementsAs(filteredWithCollectionUtils)
+            .hasSameElementsAs(filteredWithEclipseCollections)
+            .hasSameElementsAs(filteredWithEclipseCollectionsUsingIterate)
+            .hasSameElementsAs(filteredWithEclipseCollectionsUsingIterate)
+            .hasSameElementsAs(filteredWithGuava)
+            .hasSameElementsAs(EXPECTED_EVEN_FILTERED_COLLECTION);
+    }
+
+}