public class Dog extends Animal { @Override public void sound() { System.out.println("Woof!"); } }

public interface Observer { void update(String message); }

public interface Duck { void quack(); }

Dive Into Design Patterns Pdf Github Top -

public class Dog extends Animal { @Override public void sound() { System.out.println("Woof!"); } }

public interface Observer { void update(String message); } dive into design patterns pdf github top

public interface Duck { void quack(); }