如何从Java中的Decorator Pattern中删除装饰对象
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？ 什么是更好的方法？
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 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; } }
一种更好的方法是将“removeDecorator”方法添加到ComponentDecorator类中。
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。
我怀疑我误解了你的问题，但是要将装饰的（内部）对象从装饰器中取出，你可以向装饰器添加一个get方法。 加
public abstract Computer getDecorated();
到ComponentDecorator和
public Computer getDecorated(){return computer;}
到每个子类（CD，监视器，……）。 那是你在找什么？
向接口添加两个方法，undecorate（）和removeDecoration（String className）：
ThingInterface.java
public interface ThingInterface { public ThingInterface undecorate(); public ThingInterface removeDecoration(String className); public String nonDecoratedString(); public String decoratedString(); }
您的基类将仅为这些方法返回自己：
BaseThing.java
public class BaseThing implements ThingInterface { private String basicString; public BaseThing(String string) { basicString = string; } @Override public ThingInterface undecorate() { return this; } @Override public ThingInterface removeDecoration(String className) { return this; } @Override public String nonDecoratedString() { return basicString; } @Override public String decoratedString() { return basicString; } }
现在你需要的真正的东西是抽象类：
AbstractThingDecorator.java
public abstract class AbstractThingDecorator implements ThingInterface { private ThingInterface thing; public AbstractThingDecorator(ThingInterface thing) { this.thing = thing; } @Override public ThingInterface removeDecoration(String className) { ThingInterface undecorate = this; if(this.getClass().getName() == className) { undecorate = this.undecorate(); } else { ArrayList classStack = new ArrayList(); while(undecorate != undecorate.undecorate()) { if(undecorate.getClass().getName() != className) { classStack.add(undecorate.getClass().getName()); } undecorate = undecorate.undecorate(); } for(int i = classStack.size()-1;i == 0;i--) { try { Class clazz = Class.forName(classStack.get(i)); Constructor ctor = clazz.getConstructor(ThingInterface.class); Object object = ctor.newInstance(new Object[] { undecorate }); undecorate = (ThingInterface) object; } catch(Exception e) { System.out.println("Exception:" + e.getMessage()); } } } return undecorate; } @Override public ThingInterface undecorate() { return this.thing; } @Override public String nonDecoratedString() { return thing.nonDecoratedString(); } @Override public String decoratedString() { return thing.decoratedString(); } }
我正在添加两个简单的装饰器，ThingDecorator和FancyThingDecorator：
ThingDecorator.java
public class ThingDecorator extends AbstractThingDecorator { public ThingDecorator(ThingInterface thing) { super(thing); } @Override public ThingInterface undecorate() { return super.undecorate(); } @Override public String decoratedString() { return super.decoratedString() + ", decorated"; } }
FancyThingDecorator.java
public class FancyThingDecorator extends AbstractThingDecorator { public FancyThingDecorator(ThingInterface thing) { super(thing); } @Override public ThingInterface undecorate() { return super.undecorate(); } @Override public String decoratedString() { return super.decoratedString() + ", fancy"; } }
最后，我的java主要：
Decorator.java
public class Decorator { /** * @param args */ public static void main(String[] args) { ThingInterface thing = new BaseThing("Basic string"); ThingInterface decorator = new ThingDecorator(thing); ThingInterface fancyDecorator = new FancyThingDecorator(thing); ThingInterface extraFancy = new FancyThingDecorator(new ThingDecorator(thing)); ThingInterface undecorate = new FancyThingDecorator(new ThingDecorator(thing)); System.out.println("Basic thing is: " + thing.decoratedString()+"."); System.out.println("Decorated thing is: " + decorator.decoratedString()+"."); System.out.println("Fancy thing is: " + fancyDecorator.decoratedString()+"."); System.out.println("Decorated fancy thing is: " + extraFancy.decoratedString()+"."); while(extraFancy.undecorate() != extraFancy) { extraFancy = extraFancy.undecorate(); System.out.println("Rolling back decorations: " + extraFancy.decoratedString()+"."); } System.out.println("Decoration chain before removal is: " + undecorate.decoratedString()); System.out.println("Removing decoration for " + ThingDecorator.class.getName()); undecorate = undecorate.removeDecoration(ThingDecorator.class.getName()); System.out.println("Decoration chain after removal is: " + undecorate.decoratedString()+"."); } }
输出是：
基本的东西是：基本字符串。
装饰的东西是：基本字符串，装饰。
花哨的是：基本字符串，花哨。
装饰花哨的东西是：基本的字符串，装饰，花哨。
回滚装饰：基本字符串，装饰。
回滚装饰：基本字符串。
拆卸前的装饰链是：基本字符串，装饰，花式
删除ThingDecorator的装饰
拆除后的装饰链是：基本字符串，花式。