abstract class Component {
  abstract public void operation();
}

public class ConcreteComponent extends Component {
  public void operation() {
    System.out.println("ConcreteComponent operation()メソッド");
  }
}

abstract class Decorator extends Component {
  protected Component component;

  public void setComponent(Component component) {
    this.component = component;
  }

  public void operation() {
    if (component!=null) {
      component.operation();
    }
  }
}

public class ConcreteDecoratorA extends Decorator {
  private String addedState;

  public void operation() {
    super.operation();
    addedState = "new state";
    System.out.println("ConcreteDecoratorA operation()メソッド");
  }
}

public class ConcreteDecoratorB extends Decorator {
  public void operation() {
    super.operation();
    addedBehavior();
    System.out.println("ConcreteDecoratorB operation()メソッド");
  }
  private void addedBehavior() {

  }
}

public class Client {
  public static void main(String[] args) {
    ConcreteComponent c = new ConcreteComponent();
    ConcreteDecoratorA da = new ConcreteDecoratorA();
    ConcreteDecoratorB db = new ConcreteDecoratorB();

    da.setComponent(c);
    db.setComponent(da);

    db.operation();
  }
}

C:\JavaHello\Decorator>java Client
ConcreteComponent operation()メソッド
ConcreteDecoratorA operation()メソッド
ConcreteDecoratorB operation()メソッド

C:\JavaHello\Decorator>