BAEL-5621 Combining two byte arrays (#14129)

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* BAEL-5321 Initial commit

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core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/arrayconcat/CombiningByteArrays.java

@@ -0,0 +1,49 @@
+package com.baeldung.arrayconcat;
+
+import com.google.common.primitives.Bytes;
+import org.apache.commons.lang3.ArrayUtils;
+
+import java.nio.ByteBuffer;
+
+public class CombiningByteArrays {
+
+    public byte[] combineArraysUsingArrayCopy(byte[] first, byte[] second) {
+        byte[] combined = new byte[first.length + second.length];
+
+        System.arraycopy(first, 0, combined, 0, first.length);
+        System.arraycopy(second, 0, combined, first.length, second.length);
+        return combined;
+    }
+
+    public byte[] combineArraysUsingByteBuffer(byte[] first, byte[] second, byte[] third) {
+        byte[] combined = new byte[first.length + second.length + third.length];
+
+        ByteBuffer buffer = ByteBuffer.wrap(combined);
+        buffer.put(first);
+        buffer.put(second);
+        buffer.put(third);
+        return buffer.array();
+    }
+
+    public byte[] combineArraysUsingCustomMethod(byte[] first, byte[] second) {
+        byte[] combined = new byte[first.length + second.length];
+
+        for (int i = 0; i < combined.length; ++i) {
+            combined[i] = i < first.length ? first[i] : second[i - first.length];
+        }
+        return combined;
+    }
+
+    public byte[] combineArraysUsingGuava(byte[] first, byte[] second, byte[] third) {
+        byte[] combined = Bytes.concat(first, second, third);
+
+        return combined;
+    }
+
+    public byte[] combineArraysUsingApacheCommons(byte[] first, byte[] second) {
+        byte[] combined = ArrayUtils.addAll(first, second);
+
+        return combined;
+    }
+
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arrayconcat/CombiningByteArraysUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.arrayconcat;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class CombiningByteArraysUnitTest {
+
+    CombiningByteArrays combiningByteArrays;
+
+    @Before
+    public void init() {
+        combiningByteArrays = new CombiningByteArrays();
+    }
+
+    @Test
+    public void givenTwoArrays_whenCombinedUsingArraysCopy_thenArrayContainingAllElementsMustBeReturned() {
+        byte[] first = {69, 121, 101, 45, 62, 118, 114};
+        byte[] second = {58, 120, 100, 46, 64, 114, 103, 117};
+
+        byte[] combined = combiningByteArrays.combineArraysUsingArrayCopy(first, second);
+
+        byte[] expectedArray = {69, 121, 101, 45, 62, 118, 114, 58, 120, 100, 46, 64, 114, 103, 117};
+        assertArrayEquals(expectedArray, combined);
+    }
+
+    @Test
+    public void givenTwoArrays_whenCombinedUsingByteBuffer_thenArrayContainingAllElementsMustBeReturned() {
+        byte[] first = {69, 121, 101, 45};
+        byte[] second = {64, 114, 103, 117};
+        byte[] third = {11, 22, 33};
+
+        byte[] combined = combiningByteArrays.combineArraysUsingByteBuffer(first, second, third);
+
+        byte[] expectedArray = {69, 121, 101, 45, 64, 114, 103, 117, 11, 22, 33};
+        assertArrayEquals(expectedArray, combined);
+    }
+
+    @Test
+    public void givenTwoArrays_whenCombinedUsingCustomMethod_thenArrayContainingAllElementsMustBeReturned() {
+        byte[] first = {101, 45, 62 };
+        byte[] second = {58, 120, 100, 46, 64, 114};
+
+        byte[] combined = combiningByteArrays.combineArraysUsingCustomMethod(first, second);
+
+        byte[] expectedArray = {101, 45, 62, 58, 120, 100, 46, 64, 114};
+        assertArrayEquals(expectedArray, combined);
+    }
+
+    @Test
+    public void givenTwoArrays_whenCombinedUsingGuava_thenArrayContainingAllElementsMustBeReturned() {
+        byte[] first = {69, 121, 101, 118, 114};
+        byte[] second = {58, 120, 114, 103, 117};
+        byte[] third = {11, 22, 33};
+
+        byte[] combined = combiningByteArrays.combineArraysUsingGuava(first, second, third);
+
+        byte[] expectedArray = {69, 121, 101, 118, 114, 58, 120, 114, 103, 117, 11, 22, 33};
+        assertArrayEquals(expectedArray, combined);
+    }
+
+    @Test
+    public void givenTwoArrays_whenCombinedUsingApacheCommons_thenArrayContainingAllElementsMustBeReturned() {
+        byte[] first = {45, 62, 114};
+        byte[] second = {58, 120, 100};
+
+        byte[] combined = combiningByteArrays.combineArraysUsingApacheCommons(first, second);
+
+        byte[] expectedArray = {45, 62, 114, 58, 120, 100};
+        assertArrayEquals(expectedArray, combined);
+    }
+}