onReceive callback

src/Main.java

@@ -11,7 +11,7 @@ public class Main {
     public static void main(String[] args) {
         Subscriber subscriber = new Out();
         Game game = new Game(10, 2, subscriber);
+        subscriber.onReceive(s -> { System.out.println(s); return null; });
         game.players.play();
-        System.out.println(subscriber.toString());
     }
 }

src/Out.java

@@ -1,9 +1,17 @@
 import java.util.ArrayList;
+import java.util.function.Function;
 
 /**
  * The type Out.
  */
 public class Out implements Subscriber {
+    Function<String, Void> callback = new Function<String, Void>() {
+        @Override
+        public Void apply(String s) {
+            return null;
+        }
+    };
+
     /**
      * The Output.
      */
@@ -35,5 +43,10 @@ public class Out implements Subscriber {
 
     public void receive(String message) {
         output.add(message);
+        callback.apply(message);
+    }
+
+    public void onReceive(Function<String, Void> callback) {
+        this.callback = callback;
     }
 }

src/Subscriber.java

@@ -1,5 +1,9 @@
+import java.util.function.Function;
+
 public interface Subscriber {
     void receive(String message);
 
     String toString();
+
+    void onReceive(Function<String, Void> callback);
 }