如何从Java中的Decorator Pattern中删除装饰对象

Question

我正在读"傻瓜设计模式".我阅读并练习了装饰模式.使用Decorator Pattern,我们可以用任何东西装饰一个对象.现在,我想在装饰之前删除装饰对象.我已经通过ArrayList解决了这个问题,但我仍觉得它不好.你能告诉我如何删除装饰物吗？什么是更好的方式？

这是我的方式:

Computer.java

public class Computer {

    public Computer() {
    }

    public String description() {
        return "computer";
    }

}

ComponentDecorator.java

public abstract class ComponentDecorator extends Computer {
    @Override
    public abstract String description();
}

CD.java

public class CD extends ComponentDecorator {
    private Computer computer;

    public CD() {
    }

    public CD(Computer computer) {
        this.computer = computer;
    }

    @Override
    public String description() {
        return computer.description() + " and a CD";
    }

}

Disk.java

public class Disk extends ComponentDecorator {
    private Computer computer;

    public Disk() {
    }

    public Disk(Computer c) {
        computer = c;
    }

    @Override
    public String description() {
        return computer.description() + " and a disk";
    }

}

Monitor.java

public class Monitor extends ComponentDecorator {
    private Computer computer;

    public Monitor() {
    }

    public Monitor(Computer computer) {
        this.computer = computer;
    }

    @Override
    public String description() {
        return computer.description() + " and a monitor";
    }

}

Main.java

import java.util.ArrayList;
import java.util.Arrays;

public class Main {
    static ArrayList<ComponentDecorator> list = new ArrayList<>();

    public static void main(String[] args) {
        addComponent(new CD(), new Disk(), new Monitor());
        System.out.println(list.size());
        Computer penIII = getComputer();
        removeComponent(new Monitor());
        penIII = getComputer();
        System.out.println(penIII.description());
    }

    private static void addComponent(ComponentDecorator... comp) {
        list.addAll(Arrays.asList(comp));
    }

    private static void removeComponent(ComponentDecorator comp) {
        for(ComponentDecorator c : list) {
            if(c.getClass() == comp.getClass()) {
                list.remove(list.indexOf(c));
                break;
            }
        }
    }

    private static Computer getComputer() {
        Computer c = new Computer();
        Class e;
        for(ComponentDecorator d : list) {
            e = d.getClass();
            try {
                c = (Computer) e.getConstructor(new Class[]{Computer.class}).newInstance(c);
            } catch(Exception ex) {
                ex.printStackTrace();
            }
        }
        return c;
    }
}

Answer 1

一种更好的方法是将"removeDecorator"方法添加到ComponentDecorator类.

public abstract class ComponentDecorator {

private ComponentDecorator subject;

public ComponentDecorator(ComponentDecorator subject) {
  this.subject = subject;
}

@Override
public abstract String description();
}

public void removeDecorator(ComponentDecorator toRemove) {
  if (subject == null) {
    return;
  } else if (subject.equals(toRemove)) {
    subject = subject.getSubject();
  } else {
    subject.removeDecorator(toRemove);
  }
}

public ComponentDecorator getSubject() {
  return subject;
}


// Computer
public class Computer extends ComponentDecorator{

public Computer() {
  super(null);
}

public String description() {
  return "computer";
}

// CD
public class CD extends ComponentDecorator {

  public CD(ComponentDecorator computer) {
    super(computer);
  }

  @Override
  public String description() {
    return getSubject().description() + " and a CD";
  }
}

// main
public static void main(String[] args) {
    ComponentDecorator penIII = new Computer();
    penIII = new CD(penIII);
    penIII = new Monitor(penIII);
    System.out.println(penIII.description());
}

}

如果您没有要删除的装饰器的引用,则可以创建另一个类而不是类.

但是,您需要将装饰对象设置为"ComponentDecorator"而不是"Computer".我建议让Computer类扩展ComponentDecorator而不是相反.

Answer 2

我怀疑我误解了你的问题，但是为了从装饰器中获取装饰的（内部）对象，你只需向装饰器添加一个 get 方法即可。添加

public abstract Computer getDecorated();

到 ComponentDecorator 和

public Computer getDecorated(){return computer;}

每个子类（CD、监视器……）。这就是您要找的吗？