Bael-667 Flatten Nested Collections (#1330)

* article Bael-667 initial commit.

* Switch to use logging framework for output.

core-java/src/main/java/com/baeldung/list/flattennestedlist/FlattenNestedList.java

@@ -0,0 +1,17 @@
+package com.baeldung.list.flattennestedlist;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class FlattenNestedList {
+
+    public List<String> flattenListOfLists(List<List<String>> lol) {
+
+        // flatten the list
+        List<String> ls = new ArrayList<>();
+        lol.forEach((k) -> ls.addAll(k));
+
+        return ls;
+    }
+
+}