这是装饰器模式的正确实现吗？答案

【问题标题】：Is this a correct implementation of the Decorator pattern?这是装饰器模式的正确实现吗？
【发布时间】：2011-09-08 03:12:10
【问题描述】：

Main.java

package com.example.decorator;

public class Main {
    public static void main(String[] args) {
        Response response = new Response();
        View head = new View("<title>Hello, world!</title>");
        View body = new View("<h1>Hello, world!</h1>");
        response.setContent(new HtmlLayout(head, body));
        response.render();
    }
}

Response.java

package com.example.decorator;

public class Response {
    private Response content;
    public Response () {}
    public <T extends Response> void setContent(T content) {
        this.content = content;
    }
    public void render() {
        this.content.render();
    };
}

View.java

package com.example.decorator;

public class View extends Response {
    private String content;
    public View(String content) {
        this.content = content;
    }
    public void setContent(String content) {
        this.content = content;
    }
    public String getContent() {
        return this.content;
    }
    public void render() {
        System.out.println(this.content);
    }
}

Layout.java

package com.example.decorator;

public class Layout extends Response {
    private Response view;
    public <T extends Response> Layout(T view) {
        this.view = view;
    }
    public void render() {
        this.view.render();
    }
}

HtmlLayout.java

package com.example.decorator;

public class HtmlLayout extends Response {
    private Response head;
    private Response body;
    public <T extends Response> HtmlLayout(T head, T body) {
        this.head = head;
        this.body = body;
    }
    public void render() {
        System.out.println("<!doctype html>");
        System.out.println("<html>");
        System.out.println("<head>");
        this.head.render();
        System.out.println("</head>");
        System.out.println("<body>");
        this.body.render();
        System.out.println("</body>");
        System.out.println("</html>");
    }
}

【问题讨论】：

标签： java design-patterns decorator

【解决方案1】：

就我所看到的简短而言：

将您的响应更改为界面
您的 View.java 确实与装饰器模式不匹配，因此请删除 Response 的扩展，例如

最好的问候

【讨论】：

【解决方案2】：

当您希望类型（接口）A 的对象比当前做的更多时，使用装饰器模式。一个例子是：适合您的物理屏幕的网页（逻辑屏幕）不需要滚动条。但是，如果页面（逻辑屏幕）不适合物理屏幕，则必须用滚动条装饰它。用 GOF 的话来说：Decorator 的目的是动态地为对象附加额外的职责。

在如下代码中：

interface LogicalScreen {
  void render(String physical );
}

一个实现：

class SimpleScreen implements LogicalScreen {
  public void render(String physical) {
    // render itself
  }
}

装饰器的实现：

class ScreenWithScrollbar implements LogicalScreen {
  private final LogicalScreen decoratd;

  public ScreenWithScrollbar(LogicalScreen decorated) {
    this.decoratd = decorated;
  }

  public void render(String physical) {
    // render scroll bar
    // ...
    // render the decorated
    decoratd.render(physical);
    // eventually do some more stuff
  }

  public doScroll() {}
}

如何接线：

public class WhatIsDecorator {
  public static void main(String[] args) {
    LogicalScreen l1 = new SimpleScreen();
    LogicalScreen ds = new ScreenWithScrollbar(l1);

    ds.render("MyMonitor");
  }
}

您可以根据需要进行尽可能多的链接。 Decorator2(Decorator1(Simple)) ...

【讨论】：