Add undo capability

src/main/java/nl/lengrand/patterns/command/Command.java

@@ -4,4 +4,5 @@ public interface Command {
 
     void execute();
 
+    void undo();
 }

src/main/java/nl/lengrand/patterns/command/EmptyCommand.java

@@ -5,4 +5,9 @@ public class EmptyCommand implements Command{
     public void execute() {
         System.out.println("No Command");
     }
+
+    @Override
+    public void undo() {
+        System.out.println("No Command undo");
+    }
 }

src/main/java/nl/lengrand/patterns/command/LightOff.java

@@ -14,4 +14,9 @@ public class LightOff implements Command {
     public void execute() {
         light.off();
     }
+
+    @Override
+    public void undo() {
+        light.on();
+    }
 }

src/main/java/nl/lengrand/patterns/command/LightOn.java

@@ -14,4 +14,10 @@ public class LightOn implements Command {
     public void execute() {
         light.on();
     }
+
+    @Override
+    public void undo() {
+        light.off();
+    }
+
 }

src/main/java/nl/lengrand/patterns/command/RemoteControl.java

@@ -8,13 +8,20 @@ import java.util.Map;
 public class RemoteControl {
 
     private Map<String, Command> commands = new HashMap<>();
+    private Command lastCommand = new EmptyCommand();
 
     public void addCommand(String commandName, Command command){
         commands.put(commandName, command);
     }
 
     public void pressCommand(String commandName){
-        commands.getOrDefault(commandName, new EmptyCommand()).execute();
+        Command command = commands.getOrDefault(commandName, new EmptyCommand());
+        command.execute();
+        lastCommand = command;
+    }
+
+    public void undo(){
+        lastCommand.undo();
     }
 
     @Override
@@ -33,6 +40,10 @@ public class RemoteControl {
 
         System.out.println(rc);
         rc.pressCommand("BathroomLightOn");
+        rc.undo();
+        rc.pressCommand("BathroomLightOff");
+        rc.undo();
+        rc.undo();
         rc.pressCommand("Null check");
     }
 }