From 99bebe806c3bd50eaddd5e1ab006c299ce4c9cfb Mon Sep 17 00:00:00 2001
From: Grzegorz Piwowarek <gpiwowarek@gmail.com>
Date: Sat, 18 Mar 2017 07:05:02 +0100
Subject: [PATCH] Refactor flattening lists example (#1372)

---
 .../flattennestedlist/FlattenNestedList.java  | 17 -----
 .../FlattenNestedListTest.java                | 76 +++++++++++--------
 2 files changed, 44 insertions(+), 49 deletions(-)
 delete mode 100644 core-java/src/main/java/com/baeldung/list/flattennestedlist/FlattenNestedList.java

diff --git a/core-java/src/main/java/com/baeldung/list/flattennestedlist/FlattenNestedList.java b/core-java/src/main/java/com/baeldung/list/flattennestedlist/FlattenNestedList.java
deleted file mode 100644
index 11ee66560b..0000000000
--- a/core-java/src/main/java/com/baeldung/list/flattennestedlist/FlattenNestedList.java
+++ /dev/null
@@ -1,17 +0,0 @@
-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;
-    }
-
-}
diff --git a/core-java/src/test/java/com/baeldung/list/flattennestedlist/FlattenNestedListTest.java b/core-java/src/test/java/com/baeldung/list/flattennestedlist/FlattenNestedListTest.java
index 09bfdae9a5..cf9334954b 100644
--- a/core-java/src/test/java/com/baeldung/list/flattennestedlist/FlattenNestedListTest.java
+++ b/core-java/src/test/java/com/baeldung/list/flattennestedlist/FlattenNestedListTest.java
@@ -1,52 +1,64 @@
 package com.baeldung.list.flattennestedlist;
 
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.stream.Collectors;
+
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-
-import org.junit.Before;
-import org.junit.Test;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 public class FlattenNestedListTest {
 
-    private static final Logger LOGGER = LoggerFactory.getLogger(FlattenNestedListTest.class);
-    private FlattenNestedList flol;
-    
-    @Before
-    public void setup() {
-        flol = new FlattenNestedList();
-    }
-    
     @Test
-    public void givenListOfListOfString_flattenNestedList() {
-
-        // create the list to flatten
+    public void givenListOfListOfString_flattenNestedList1() {
+        // given
         List<String> ls1 = Arrays.asList("one:one", "one:two", "one:three");
         List<String> ls2 = Arrays.asList("two:one", "two:two", "two:three");
         List<String> ls3 = Arrays.asList("three:one", "three:two", "three:three");
 
-        List<List<String>> lol = new ArrayList<>();
-        lol.addAll(Arrays.asList(ls1, ls2, ls3));
-        
-        // show nested list
-        LOGGER.debug("\nNested list: ");
-        lol.forEach((nl) -> LOGGER.debug(nl + ""));
+        List<List<String>> list = Arrays.asList(ls1, ls2, ls3);
 
-        // flatten it
-        List<String> ls = flol.flattenListOfLists(lol);
+        // when
+        List<String> ls = flattenListOfListsImperatively(list);
 
+        // then
         assertNotNull(ls);
         assertTrue(ls.size() == 9);
-        
-        // show flattened list
-        LOGGER.debug("\nFlattened list:");
-        ls.forEach((l) -> LOGGER.debug(l));
+        //TODO content assertion
+    }
 
+    @Test
+    public void givenListOfListOfString_flattenNestedList2() {
+        // given
+        List<String> ls1 = Arrays.asList("one:one", "one:two", "one:three");
+        List<String> ls2 = Arrays.asList("two:one", "two:two", "two:three");
+        List<String> ls3 = Arrays.asList("three:one", "three:two", "three:three");
+
+        List<List<String>> list = Arrays.asList(ls1, ls2, ls3);
+
+        // when
+        List<String> ls = flattenListOfListsStream(list);
+
+        // then
+        assertNotNull(ls);
+        assertTrue(ls.size() == 9);
+        //TODO content assertion
+    }
+
+    public <T> List<T> flattenListOfListsImperatively(List<List<T>> list) {
+        List<T> ls = new ArrayList<>();
+        list.forEach(ls::addAll);
+        return ls;
+    }
+
+    public <T> List<T> flattenListOfListsStream(List<List<T>> list) {
+        return list.stream()
+          .flatMap(Collection::stream)
+          .collect(Collectors.toList());
     }
 
 }