[BAEL-1775] Getting size of Iterable in Java

core-java-collections/src/main/java/com/baeldung/java/iterable/IterableSize.java

@@ -0,0 +1,65 @@
+package com.baeldung.java.iterable;
+
+import java.util.Collection;
+import java.util.stream.StreamSupport;
+
+import org.apache.commons.collections4.IterableUtils;
+
+import com.google.common.collect.Iterables;
+
+/**
+ * Provides methods for getting the size of an {@link Iterable} object.
+ */
+public class IterableSize {
+
+    /**
+     * Get the size of {@code Iterable} using Java 7.
+     *
+     * @param data the iterable
+     * @return the size of the iterable
+     */
+    public static int sizeUsingJava7(final Iterable data) {
+
+        if (data instanceof Collection) {
+            return ((Collection<?>) data).size();
+        }
+        int counter = 0;
+        for (final Object i : data) {
+            counter++;
+        }
+        return counter;
+    }
+
+    /**
+     * Get the size of {@code Iterable} using Java 8.
+     *
+     * @param data the iterable
+     * @return the size of the iterable
+     */
+    public static long sizeUsingJava8(final Iterable data) {
+
+        return StreamSupport.stream(data.spliterator(), false).count();
+    }
+
+    /**
+     * Get the size of {@code Iterable} using Apache Collections.
+     *
+     * @param data the iterable
+     * @return the size of the iterable
+     */
+    public static int sizeUsingApacheCollections(final Iterable data) {
+
+        return IterableUtils.size(data);
+    }
+
+    /**
+     * Get the size of {@code Iterable} using Google Guava.
+     *
+     * @param data the iterable
+     * @return the size of the iterable
+     */
+    public static int sizeUsingGoogleGuava(final Iterable data) {
+
+        return Iterables.size(data);
+    }
+}

core-java-collections/src/test/java/com/baeldung/java/iterable/IterableSizeTest.java

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+package com.baeldung.java.iterable;
+
+import static org.junit.Assert.assertEquals;
+
+import java.sql.SQLException;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import com.google.common.collect.Lists;
+
+class IterableSizeTest {
+
+    private final List<String> list = Lists.newArrayList("Apple", "Orange", "Banana");
+
+    private Iterable data;
+
+    @Test
+    void whenUsingJava7_iterableOfCollectionType_thenCorrectSize() {
+
+        final int size = IterableSize.sizeUsingJava7(list);
+
+        assertEquals(3, size);
+    }
+
+    @Test
+    void whenUsingJava7_iterableNotOfCollectionType_thenCorrect() {
+
+        final SQLException exception = new SQLException();
+        exception.setNextException(new SQLException());
+        final int size = IterableSize.sizeUsingJava7(exception);
+
+        assertEquals(2, size);
+    }
+
+    @Test
+    void whenUsingJava8_thenCorrect() {
+
+        final long size = IterableSize.sizeUsingJava8(list);
+
+        assertEquals(3, size);
+    }
+
+    @Test
+    void whenUsingApacheCollections_thenCorrect() {
+
+        final int size = IterableSize.sizeUsingApacheCollections(list);
+
+        assertEquals(3, size);
+    }
+
+    @Test
+    void whenUsingGoogleGuava_thenCorrect() {
+
+        final int size = IterableSize.sizeUsingGoogleGuava(list);
+
+        assertEquals(3, size);
+    }
+}