System.out.println("19. Observer: ");
Subject subject = new Subject().attach(new HelloWorldObserver());
subject.notifyObservers();
System.out.println("20. State: ");
HelloWorldStateContext helloWorldStateContext = new HelloWorldStateContext();
HelloWorld stateHelloWorld = helloWorldStateContext.appendWord("Hello").appendWord("State");
System.out.println(stateHelloWorld.helloWorld());
System.out.println("21. Strategy: ");
HelloWorldStrategyContext helloWorldStrategyContext = new HelloWorldStrategyContext(new DesignPatternHelloWorldStrategy());
System.out.println(helloWorldStrategyContext.helloWorld());