BAEL-1328 (#3099)

* BAEL-1328 How to Invert an Array in Java

* Removing code from evaluation article.

* BAEL-1328
Adjusting spaces and implement inversion with commons lang3 and guava.

* BAEL-1328 Renaming unit test class; using AssertJ.

core-java/src/main/java/com/baeldung/array/ArrayInverter.java

@@ -0,0 +1,41 @@
+package com.baeldung.array;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.IntStream;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+import com.google.common.collect.Lists;
+
+public class ArrayInverter {
+
+    public void invertUsingFor(Object[] array) {
+        for (int i = 0; i < array.length / 2; i++) {
+            Object temp = array[i];
+            array[i] = array[array.length - 1 - i];
+            array[array.length - 1 - i] = temp;
+        }
+    }
+
+    public void invertUsingCollectionsReverse(Object[] array) {
+        List<Object> list = Arrays.asList(array);
+        Collections.reverse(list);
+    }
+
+    public Object[] invertUsingStreams(final Object[] array) {
+        return IntStream.range(1, array.length + 1).mapToObj(i -> array[array.length - i]).toArray();
+    }
+
+    public void invertUsingCommonsLang(Object[] array) {
+        ArrayUtils.reverse(array);
+    }
+
+    public Object[] invertUsingGuava(Object[] array) {
+        List<Object> list = Arrays.asList(array);
+        List<Object> reverted = Lists.reverse(list);
+        return reverted.toArray();
+    }
+
+}

core-java/src/test/java/com/baeldung/array/ArrayInverterUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.array;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class ArrayInverterUnitTest {
+
+    private String[] fruits = { "apples", "tomatoes", "bananas", "guavas", "pineapples", "oranges" };
+
+    @Test
+    public void invertArrayWithForLoop() {
+        ArrayInverter inverter = new ArrayInverter();
+        inverter.invertUsingFor(fruits);
+
+        assertThat(new String[] { "oranges", "pineapples", "guavas", "bananas", "tomatoes", "apples" }).isEqualTo(fruits);
+    }
+
+    @Test
+    public void invertArrayWithCollectionsReverse() {
+        ArrayInverter inverter = new ArrayInverter();
+        inverter.invertUsingCollectionsReverse(fruits);
+
+        assertThat(new String[] { "oranges", "pineapples", "guavas", "bananas", "tomatoes", "apples" }).isEqualTo(fruits);
+    }
+
+    @Test
+    public void invertArrayWithStreams() {
+        ArrayInverter inverter = new ArrayInverter();
+
+        assertThat(new String[] { "oranges", "pineapples", "guavas", "bananas", "tomatoes", "apples" }).isEqualTo(inverter.invertUsingStreams(fruits));
+    }
+
+    @Test
+    public void invertArrayWithCommonsLang() {
+        ArrayInverter inverter = new ArrayInverter();
+        inverter.invertUsingCommonsLang(fruits);
+
+        assertThat(new String[] { "oranges", "pineapples", "guavas", "bananas", "tomatoes", "apples" }).isEqualTo(fruits);
+    }
+
+    @Test
+    public void invertArrayWithGuava() {
+        ArrayInverter inverter = new ArrayInverter();
+
+        assertThat(new String[] { "oranges", "pineapples", "guavas", "bananas", "tomatoes", "apples" }).isEqualTo(inverter.invertUsingGuava(fruits));
+    }
+
+}