diff --git a/command/README.md b/command/README.md
index fc0a11d9f..b763cf4dd 100644
--- a/command/README.md
+++ b/command/README.md
@@ -75,19 +75,18 @@ public class Wizard {
 Next we present the spell hierarchy.
 
 ```java
-public abstract class Command {
+public interface Command {
 
-  public abstract void execute(Target target);
+  void execute(Target target);
 
-  public abstract void undo();
+  void undo();
 
-  public abstract void redo();
+  void redo();
 
-  @Override
-  public abstract String toString();
+  String toString();
 }
 
-public class InvisibilitySpell extends Command {
+public class InvisibilitySpell implements Command {
 
   private Target target;
 
@@ -117,7 +116,7 @@ public class InvisibilitySpell extends Command {
   }
 }
 
-public class ShrinkSpell extends Command {
+public class ShrinkSpell implements Command {
 
   private Size oldSize;
   private Target target;
diff --git a/command/etc/command.png b/command/etc/command.png
index 81b47d6d0..5564b0ec5 100644
Binary files a/command/etc/command.png and b/command/etc/command.png differ
diff --git a/command/etc/command.urm.puml b/command/etc/command.urm.puml
index a8b773418..c9c172226 100644
--- a/command/etc/command.urm.puml
+++ b/command/etc/command.urm.puml
@@ -4,7 +4,7 @@ package com.iluwatar.command {
     + App()
     + main(args : String[]) {static}
   }
-  abstract class Command {
+  interface Command {
     + Command()
     + execute(Target) {abstract}
     + redo() {abstract}
@@ -77,7 +77,7 @@ ShrinkSpell -->  "-oldSize" Size
 InvisibilitySpell -->  "-target" Target
 ShrinkSpell -->  "-target" Target
 Target -->  "-visibility" Visibility
-Goblin --|> Target 
-InvisibilitySpell --|> Command 
-ShrinkSpell --|> Command 
-@enduml
\ No newline at end of file
+Goblin --|> Target
+InvisibilitySpell ..|> Command
+ShrinkSpell ..|> Command
+@enduml