Fixes based on code review feedback

dirty-flag/etc/dirty-flag.ucls

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.2" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.dirtyflag.App" project="dirty-flag" 
+    file="/dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="266" y="188"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="2" language="java" name="com.iluwatar.dirtyflag.DataFetcher" project="dirty-flag" 
+    file="/dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="153" width="125" x="66" y="291"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="3" language="java" name="com.iluwatar.dirtyflag.World" project="dirty-flag" 
+    file="/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="379" y="366"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <association id="4">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="5" name="df"/>      
+      <multiplicity id="6" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

dirty-flag/pom.xml

@@ -5,11 +5,11 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0-SNAPSHOT</version>
+    <version>1.20.0-SNAPSHOT</version>
   </parent>
   <groupId>com.iluwatar</groupId>
   <artifactId>dirty-flag</artifactId>
-  <version>1.19.0-SNAPSHOT</version>
+  <version>1.20.0-SNAPSHOT</version>
   <name>dirty-flag</name>
   <url>http://maven.apache.org</url>
   <properties>

dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java

@@ -57,7 +57,7 @@ public class App {
     executorService.scheduleAtFixedRate(new Runnable() {
       @Override
       public void run() {
-        World world = World.getInstance();
+        World world = new World();
         List<String> countries = world.fetch();
         System.out.println("Our world currently has the following countries:-");
         for (String country : countries) {

dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java

@@ -15,23 +15,11 @@ import java.util.List;
  */
 public class DataFetcher {
 
-  private static DataFetcher df;
   private final String filename = "world.txt";
-  private long lastFetched = -1;
+  private long lastFetched;
 
-  private DataFetcher() {
-  }
-
-  /**
-   * Init.
-   * 
-   * @return DataFetcher instance
-   */
-  public static DataFetcher getInstance() {
-    if (df == null) {
-      df = new DataFetcher();
-    }
-    return df;
+  public DataFetcher() {
+    this.lastFetched = -1;
   }
 
   private boolean isDirty(long fileLastModified) {
@@ -66,6 +54,6 @@ public class DataFetcher {
       return data;
     }
 
-    return null;
+    return new ArrayList<String>();
   }
 }

dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java

@@ -12,22 +12,12 @@ import java.util.List;
  */
 public class World {
 
-  private static World world;
-  private static List<String> countries = new ArrayList<String>();
+  private List<String> countries;
+  private DataFetcher df;
 
-  private World() {
-  }
-
-  /**
-   * Init.
-   * 
-   * @return World instance
-   */
-  public static World getInstance() {
-    if (world == null) {
-      world = new World();
-    }
-    return world;
+  public World() {
+    this.countries = new ArrayList<String>();
+    this.df = new DataFetcher();
   }
 
   /**
@@ -37,10 +27,9 @@ public class World {
    * @return List of strings
    */
   public List<String> fetch() {
-    DataFetcher df = DataFetcher.getInstance();
     List<String> data = df.fetch();
 
-    countries = data == null ? countries : data;
+    countries = data.isEmpty() ? countries : data;
 
     return countries;
   }

dirty-flag/src/test/java/org/dirty/flag/DirtyFlagTest.java

@@ -24,10 +24,8 @@ package org.dirty.flag;
 
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import java.lang.reflect.Field;
 import java.util.List;
 
-import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import com.iluwatar.dirtyflag.DataFetcher;
@@ -39,23 +37,16 @@ import com.iluwatar.dirtyflag.DataFetcher;
  */
 public class DirtyFlagTest {
 
-  @BeforeEach
-  public void reset() throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
-    Field instance = DataFetcher.class.getDeclaredField("df");
-    instance.setAccessible(true);
-    instance.set(null, null);
-  }
-
   @Test
   public void testIsDirty() {
-    DataFetcher df = DataFetcher.getInstance();
+    DataFetcher df = new DataFetcher();
     List<String> countries = df.fetch();
     assertTrue(!countries.isEmpty());
   }
 
   @Test
   public void testIsNotDirty() {
-    DataFetcher df = DataFetcher.getInstance();
+    DataFetcher df = new DataFetcher();
     df.fetch();
     List<String> countries = df.fetch();
     assertTrue(countries == null);