Test done

extension-objects/src/main/java/App.java

@@ -38,6 +38,7 @@ public class App {
     SergeantExtension sergeantExtension = (SergeantExtension) unit.getUnitExtension("SergeantExtension");
     CommanderExtension commanderExtension = (CommanderExtension) unit.getUnitExtension("CommanderExtension");
 
+    //if unit have extension call the method
     if (soldierExtension != null) {
       soldierExtension.soldierReady();
     } else {
@@ -51,7 +52,7 @@ public class App {
     }
 
     if (commanderExtension != null) {
-      // commanderExtension.sergeantReady();
+      commanderExtension.commanderReady();
     } else {
       System.out.println(unit.getName() + " without CommanderExtension");
     }

extension-objects/src/main/java/abstractextensions/CommanderExtension.java

@@ -4,4 +4,6 @@ package abstractextensions;
  * Created by Srdjan on 27-Apr-17.
  */
 public interface CommanderExtension extends UnitExtension {
+
+  void commanderReady();
 }

extension-objects/src/main/java/concreteextensions/Commander.java

@@ -13,4 +13,9 @@ public class Commander implements CommanderExtension {
   public Commander(CommanderUnit commanderUnit) {
     this.unit = commanderUnit;
   }
+
+  @Override
+  public void commanderReady() {
+    System.out.println("[Commander] " + unit.getName() + " is ready!");
+  }
 }

extension-objects/src/main/java/concreteextensions/Sergeant.java

@@ -16,6 +16,6 @@ public class Sergeant implements SergeantExtension {
 
   @Override
   public void sergeantReady() {
-    System.out.println("[Sergeant] " + unit.getName() + " do command! ");
+    System.out.println("[Sergeant] " + unit.getName() + " is ready! ");
   }
 }

extension-objects/src/main/java/concreteextensions/Soldier.java

@@ -16,6 +16,6 @@ public class Soldier implements SoldierExtension {
 
   @Override
   public void soldierReady() {
-    System.out.println("[Solider] " + unit.getName() + "  do command");
+    System.out.println("[Solider] " + unit.getName() + "  is ready!");
   }
 }