Pr/1089 (#1100)

* String to char array and char array to String.

* Method change

* Custom ThreadPool In Java 8 Parallel Streams

* Implemented suggested edits from editor.

* Broke long method signature

* Changed primitive type int to long and formula.

* Update wrapper type to Long

* Added "Test" suffix to test class name.

core-java/src/test/java/org/baeldung/java/streams/ThreadPoolInParallelStreamTest.java

@@ -13,7 +13,7 @@ import java.util.stream.Stream;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
-public class ThreadPoolInParallelStream {
+public class ThreadPoolInParallelStreamTest {
     
     @Test
     public void giveRangeOfLongs_whenSummedInParallel_shouldBeEqualToExpectedTotal()