BAEL-886 How to add a single element to a Stream (#1887)

core-java/src/test/java/com/baeldung/stream/StreamAddUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.stream;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import static org.junit.Assert.assertEquals;
+import org.junit.Test;
+
+public class StreamAddUnitTest {
+
+    @Test
+    public void givenStream_whenAppendingObject_thenAppended() {
+        Stream<String> anStream = Stream.of("a", "b", "c", "d", "e");
+
+        Stream<String> newStream = Stream.concat(anStream, Stream.of("A"));
+
+        List<String> resultList = newStream.collect(Collectors.toList());
+        assertEquals(resultList.get(resultList.size() - 1), "A");
+    }
+
+    @Test
+    public void givenStream_whenPrependingObject_thenPrepended() {
+        Stream<Integer> anStream = Stream.of(1, 2, 3, 4, 5);
+
+        Stream<Integer> newStream = Stream.concat(Stream.of(99), anStream);
+
+        assertEquals(newStream.findFirst()
+            .get(), (Integer) 99);
+    }
+
+    @Test
+    public void givenStream_whenInsertingObject_thenInserted() {
+        Stream<Double> anStream = Stream.of(1.1, 2.2, 3.3);
+
+        Stream<Double> newStream = insertInStream(anStream, 9.9, 3);
+
+        List<Double> resultList = newStream.collect(Collectors.toList());
+        assertEquals(resultList.get(3), (Double) 9.9);
+    }
+
+    public <T> Stream<T> insertInStream(Stream<T> stream, T elem, int index) {
+        List<T> result = stream.collect(Collectors.toList());
+        result.add(index, elem);
+        return result.stream();
+    }
+}