change the flight in strategy

strategy/app.d

@@ -1,6 +1,7 @@
 module strategy.app;
 
 import strategy.duck;
+import strategy.flybehavior;
 
 void main()
 {
@@ -11,4 +12,6 @@ void main()
     Duck model = new ModelDuck;
     model.performQuack();
     model.performFly();
+    model.setFlyBehavior(new FlyRocketPowered);
+    model.performFly();
 }

strategy/duck.d

@@ -24,6 +24,16 @@ abstract class Duck
     {
         writeln("All ducks float, even decoys!");
     }
+
+    void setFlyBehavior(FlyBehavior fb)
+    {
+        flyBehavior = fb;
+    }
+
+    void setQuackBehavior(QuackBehavior qb)
+    {
+        quackBehavior = qb;
+    }
 }
 
 class MallardDuck : Duck