diff --git a/extension-objects/pom.xml b/extension-objects/pom.xml
new file mode 100644
index 000000000..afdf010a2
--- /dev/null
+++ b/extension-objects/pom.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>java-design-patterns</artifactId>
+        <groupId>com.iluwatar</groupId>
+        <version>1.16.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>extension-objects</artifactId>
+
+
+</project>
\ No newline at end of file
diff --git a/extension-objects/src/main/java/App.java b/extension-objects/src/main/java/App.java
new file mode 100644
index 000000000..9aa934580
--- /dev/null
+++ b/extension-objects/src/main/java/App.java
@@ -0,0 +1,59 @@
+import abstractextensions.CommanderExtension;
+import abstractextensions.SergeantExtension;
+import abstractextensions.SoldierExtension;
+import units.CommanderUnit;
+import units.SergeantUnit;
+import units.SoldierUnit;
+import units.Unit;
+
+/**
+ * Created by Srdjan on 26-Apr-17.
+ */
+public class App {
+
+  /**
+   * Program entry point
+   *
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+
+    //Create 3 different units
+    Unit unit = new SoldierUnit("SoldierUnit1");
+    Unit unit1 = new SergeantUnit("SergeantUnit1");
+    Unit unit2 = new CommanderUnit("CommanderUnit1");
+
+    //check for each unit to have an extension
+    checkExtensionsForUnit(unit);
+    checkExtensionsForUnit(unit1);
+    checkExtensionsForUnit(unit2);
+
+  }
+
+  private static void checkExtensionsForUnit(Unit unit) {
+    //separate for better view
+    System.out.println();
+
+    SoldierExtension soldierExtension = (SoldierExtension) unit.getUnitExtension("SoldierExtension");
+    SergeantExtension sergeantExtension = (SergeantExtension) unit.getUnitExtension("SergeantExtension");
+    CommanderExtension commanderExtension = (CommanderExtension) unit.getUnitExtension("CommanderExtension");
+
+    if (soldierExtension != null) {
+      soldierExtension.soldierReady();
+    } else {
+      System.out.println(unit.getName() + " without SoldierExtension");
+    }
+
+    if (sergeantExtension != null) {
+      sergeantExtension.sergeantReady();
+    } else {
+      System.out.println(unit.getName() + " without SergeantExtension");
+    }
+
+    if (commanderExtension != null) {
+      // commanderExtension.sergeantReady();
+    } else {
+      System.out.println(unit.getName() + " without CommanderExtension");
+    }
+  }
+}
diff --git a/extension-objects/src/main/java/abstractextensions/CommanderExtension.java b/extension-objects/src/main/java/abstractextensions/CommanderExtension.java
new file mode 100644
index 000000000..aa716a3ae
--- /dev/null
+++ b/extension-objects/src/main/java/abstractextensions/CommanderExtension.java
@@ -0,0 +1,7 @@
+package abstractextensions;
+
+/**
+ * Created by Srdjan on 27-Apr-17.
+ */
+public interface CommanderExtension extends UnitExtension {
+}
diff --git a/extension-objects/src/main/java/abstractextensions/SergeantExtension.java b/extension-objects/src/main/java/abstractextensions/SergeantExtension.java
new file mode 100644
index 000000000..dc7bbdc70
--- /dev/null
+++ b/extension-objects/src/main/java/abstractextensions/SergeantExtension.java
@@ -0,0 +1,9 @@
+package abstractextensions;
+
+/**
+ * Created by Srdjan on 27-Apr-17.
+ */
+public interface SergeantExtension extends UnitExtension {
+
+  void sergeantReady();
+}
diff --git a/extension-objects/src/main/java/abstractextensions/SoldierExtension.java b/extension-objects/src/main/java/abstractextensions/SoldierExtension.java
new file mode 100644
index 000000000..1715811f8
--- /dev/null
+++ b/extension-objects/src/main/java/abstractextensions/SoldierExtension.java
@@ -0,0 +1,8 @@
+package abstractextensions;
+
+/**
+ * Created by Srdjan on 26-Apr-17.
+ */
+public interface SoldierExtension extends UnitExtension {
+  void soldierReady();
+}
diff --git a/extension-objects/src/main/java/abstractextensions/UnitExtension.java b/extension-objects/src/main/java/abstractextensions/UnitExtension.java
new file mode 100644
index 000000000..03c58d181
--- /dev/null
+++ b/extension-objects/src/main/java/abstractextensions/UnitExtension.java
@@ -0,0 +1,7 @@
+package abstractextensions;
+
+/**
+ * Created by Srdjan on 26-Apr-17.
+ */
+public interface UnitExtension {
+}
diff --git a/extension-objects/src/main/java/concreteextensions/Commander.java b/extension-objects/src/main/java/concreteextensions/Commander.java
new file mode 100644
index 000000000..3de4d124a
--- /dev/null
+++ b/extension-objects/src/main/java/concreteextensions/Commander.java
@@ -0,0 +1,16 @@
+package concreteextensions;
+
+import abstractextensions.CommanderExtension;
+import units.CommanderUnit;
+
+/**
+ * Created by Srdjan on 27-Apr-17.
+ */
+public class Commander implements CommanderExtension {
+
+  private CommanderUnit unit;
+
+  public Commander(CommanderUnit commanderUnit) {
+    this.unit = commanderUnit;
+  }
+}
diff --git a/extension-objects/src/main/java/concreteextensions/Sergeant.java b/extension-objects/src/main/java/concreteextensions/Sergeant.java
new file mode 100644
index 000000000..b2d4485c3
--- /dev/null
+++ b/extension-objects/src/main/java/concreteextensions/Sergeant.java
@@ -0,0 +1,21 @@
+package concreteextensions;
+
+import abstractextensions.SergeantExtension;
+import units.SergeantUnit;
+
+/**
+ * Created by Srdjan on 27-Apr-17.
+ */
+public class Sergeant implements SergeantExtension {
+
+  private SergeantUnit unit;
+
+  public Sergeant(SergeantUnit sergeantUnit) {
+    this.unit = sergeantUnit;
+  }
+
+  @Override
+  public void sergeantReady() {
+    System.out.println("[Sergeant] " + unit.getName() + " do command! ");
+  }
+}
diff --git a/extension-objects/src/main/java/concreteextensions/Soldier.java b/extension-objects/src/main/java/concreteextensions/Soldier.java
new file mode 100644
index 000000000..e2d11e244
--- /dev/null
+++ b/extension-objects/src/main/java/concreteextensions/Soldier.java
@@ -0,0 +1,21 @@
+package concreteextensions;
+
+import abstractextensions.SoldierExtension;
+import units.SoldierUnit;
+
+/**
+ * Created by Srdjan on 26-Apr-17.
+ */
+public class Soldier implements SoldierExtension {
+
+  private SoldierUnit unit;
+
+  public Soldier(SoldierUnit soldierUnit) {
+    this.unit = soldierUnit;
+  }
+
+  @Override
+  public void soldierReady() {
+    System.out.println("[Solider] " + unit.getName() + "  do command");
+  }
+}
diff --git a/extension-objects/src/main/java/units/CommanderUnit.java b/extension-objects/src/main/java/units/CommanderUnit.java
new file mode 100644
index 000000000..67a0f9a06
--- /dev/null
+++ b/extension-objects/src/main/java/units/CommanderUnit.java
@@ -0,0 +1,30 @@
+package units;
+
+import abstractextensions.CommanderExtension;
+import abstractextensions.UnitExtension;
+import concreteextensions.Commander;
+
+/**
+ * Created by Srdjan on 27-Apr-17.
+ */
+public class CommanderUnit extends Unit {
+
+  private CommanderExtension commanderExtension;
+
+  public CommanderUnit(String name) {
+    super(name);
+  }
+
+  @Override
+  public UnitExtension getUnitExtension(String extensionName) {
+
+    if (extensionName.equals("CommanderExtension")) {
+      if (commanderExtension == null) {
+        commanderExtension = new Commander(this);
+      }
+      return commanderExtension;
+    }
+
+    return super.getUnitExtension(extensionName);
+  }
+}
diff --git a/extension-objects/src/main/java/units/SergeantUnit.java b/extension-objects/src/main/java/units/SergeantUnit.java
new file mode 100644
index 000000000..3188f7e4e
--- /dev/null
+++ b/extension-objects/src/main/java/units/SergeantUnit.java
@@ -0,0 +1,30 @@
+package units;
+
+import abstractextensions.SergeantExtension;
+import abstractextensions.UnitExtension;
+import concreteextensions.Sergeant;
+
+/**
+ * Created by Srdjan on 27-Apr-17.
+ */
+public class SergeantUnit extends Unit {
+
+  private SergeantExtension sergeantExtension;
+
+  public SergeantUnit(String name) {
+    super(name);
+  }
+
+  @Override
+  public UnitExtension getUnitExtension(String extensionName) {
+
+    if (extensionName.equals("SergeantExtension")) {
+      if (sergeantExtension == null) {
+        sergeantExtension = new Sergeant(this);
+      }
+      return sergeantExtension;
+    }
+
+    return super.getUnitExtension(extensionName);
+  }
+}
diff --git a/extension-objects/src/main/java/units/SoldierUnit.java b/extension-objects/src/main/java/units/SoldierUnit.java
new file mode 100644
index 000000000..f96842465
--- /dev/null
+++ b/extension-objects/src/main/java/units/SoldierUnit.java
@@ -0,0 +1,30 @@
+package units;
+
+import abstractextensions.SoldierExtension;
+import abstractextensions.UnitExtension;
+import concreteextensions.Soldier;
+
+/**
+ * Created by Srdjan on 26-Apr-17.
+ */
+public class SoldierUnit extends Unit {
+
+  private SoldierExtension soldierExtension;
+
+  public SoldierUnit(String name) {
+    super(name);
+  }
+
+  @Override
+  public UnitExtension getUnitExtension(String extensionName) {
+
+    if (extensionName.equals("SoldierExtension")) {
+      if (soldierExtension == null) {
+        soldierExtension = new Soldier(this);
+      }
+
+      return soldierExtension;
+    }
+    return super.getUnitExtension(extensionName);
+  }
+}
diff --git a/extension-objects/src/main/java/units/Unit.java b/extension-objects/src/main/java/units/Unit.java
new file mode 100644
index 000000000..670c60aa8
--- /dev/null
+++ b/extension-objects/src/main/java/units/Unit.java
@@ -0,0 +1,27 @@
+package units;
+
+import abstractextensions.UnitExtension;
+
+/**
+ * Created by Srdjan on 26-Apr-17.
+ */
+public class Unit {
+
+  private String name;
+
+  public Unit(String name) {
+    this.name = name;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
+
+  public UnitExtension getUnitExtension(String extensionName) {
+    return null;
+  }
+}
diff --git a/pom.xml b/pom.xml
index a45f0e1f3..dab143e8b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -139,6 +139,7 @@
         <module>converter</module>
         <module>guarded-suspension</module>
         <module>balking</module>
+        <module>extension-objects</module>
     </modules>
 
     <dependencyManagement>