BAEL-6100-Add-example-code-for-integer-array-to-strings-using-streams… (#13375)

* BAEL-6100-Add-example-code-for-integer-array-to-strings-using-streams-tutorial

* BAEL-6100 remove wrongly added README update

* BAEL-6100 Add interger array to single string example

* BAEL-6100 Correct typo in test class name

core-java-modules/core-java-streams-4/src/main/java/com/baeldung/streams/intarraytostrings/ArrayConversionUtils.java

@@ -0,0 +1,43 @@
+package com.baeldung.streams.intarraytostrings;
+
+import java.util.Arrays;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class ArrayConversionUtils {
+
+    public static void createStreamExample() {
+        int[] intArray = { 1, 2, 3, 4, 5 };
+        IntStream intStream = Arrays.stream(intArray);
+
+        Integer[] integerArray = { 1, 2, 3, 4, 5 };
+        Stream<Integer> integerStream = Arrays.stream(integerArray);
+    }
+
+    public static String[] convertToStringArray(Integer[] input) {
+        return Arrays.stream(input)
+          .map(Object::toString)
+          .toArray(String[]::new);
+    }
+
+    public static String[] convertToStringArray(int[] input) {
+        return Arrays.stream(input)
+          .mapToObj(Integer::toString)
+          .toArray(String[]::new);
+    }
+
+    public static String[] convertToStringArrayWithBoxing(int[] input) {
+        return Arrays.stream(input)
+          .boxed()
+          .map(Object::toString)
+          .toArray(String[]::new);
+    }
+
+    public static String convertToString(int[] input){
+        return Arrays.stream(input)
+          .mapToObj(Integer::toString)
+          .collect(Collectors.joining(", "));
+    }
+
+}

core-java-modules/core-java-streams-4/src/test/java/com/baeldung/streams/intarraytostrings/IntArrayToStringUnitTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.streams.intarraytostrings;
+
+import static com.baeldung.streams.intarraytostrings.ArrayConversionUtils.convertToString;
+import static com.baeldung.streams.intarraytostrings.ArrayConversionUtils.convertToStringArray;
+import static com.baeldung.streams.intarraytostrings.ArrayConversionUtils.convertToStringArrayWithBoxing;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class IntArrayToStringUnitTest {
+
+    @Test
+    public void whenConvertingIntegers_thenHandleStreamOfIntegers() {
+        Integer[] integerNumbers = { 1, 2, 3, 4, 5 };
+        String[] expectedOutput = { "1", "2", "3", "4", "5" };
+
+        String[] strings = convertToStringArray(integerNumbers);
+
+        Assert.assertArrayEquals(expectedOutput, strings);
+    }
+
+    @Test
+    public void whenConvertingInts_thenHandleIntStream() {
+        int[] intNumbers = { 1, 2, 3, 4, 5 };
+        String[] expectedOutput = { "1", "2", "3", "4", "5" };
+
+        String[] strings = convertToStringArray(intNumbers);
+
+        Assert.assertArrayEquals(expectedOutput, strings);
+    }
+
+    @Test
+    public void givenAnIntArray_whenBoxingToInteger_thenHandleStreamOfIntegers() {
+        int[] intNumbers = { 1, 2, 3, 4, 5 };
+        String[] expectedOutput = { "1", "2", "3", "4", "5" };
+
+        String[] strings = convertToStringArrayWithBoxing(intNumbers);
+
+        Assert.assertArrayEquals(expectedOutput, strings);
+    }
+
+    @Test
+    public void givenAnIntArray_whenUsingCollectorsJoining_thenReturnCommaSeparatedString(){
+        int[] intNumbers = { 1, 2, 3, 4, 5 };
+        String expectedOutput = "1, 2, 3, 4, 5";
+
+        String string = convertToString(intNumbers);
+
+        Assert.assertEquals(expectedOutput, string);
+    }
+
+}