Decorator Pattern(裝飾模式)

• Definition

The Decorator Pattern attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

• Class Diagram

• Component Role

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

• ConcreteComponent Role

public class ConcreteComponent extends Component {
    @Override
    public void operate() {
        System.out.println("do Something");
    }
}

• Decorator Role

public abstract class Decorator extends Component {
    private Component _component;
    
    public Decorator(Component component) {
        this._component = component;
    }

    @Override
    public void operate() {
        this._component.operate();
    }
}

• ConcreteDecorator Role

public class ConcreteDecorator1 extends Decorator {

    public ConcreteDecorator1(Component component)
        super(component);
    }

    private void method1() {
        System.out.println("method1 Decorator");
    }

    public void operate() {    
        this.method1();
        super.operate();
    }
}

public class ConcreteDecorator2 extends Decorator {

    public ConcreteDecorator2(Component component)
        super(component);
    }

    private void method2() {
        System.out.println("method2 Decorator");
    }

    public void operate() {    
        this.method2();
        super.operate();
    }
}

• Client Role

public class Client {
    public static void main(String[] args) {
        Component component = new ConcreteComponent();
        component = new ConcreteDecorator1(component);
         component = new ConcreteDecorator2(component);
        component.operate();
    }
}