Home Java javaTutorial Implementation case of Java Decorator pattern

Implementation case of Java Decorator pattern

Mar 10, 2017 pm 01:17 PM

In Java, many classes under the io package are the embodiment of the typical decorator pattern, such as:

new BufferedOutputStream(OutputStream out)
new BufferedInputStream(InputStream in);
new PrintWriter(OutputStream out)
new FilterReader(Reader in);
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The decorated class implements the same interface as the decorated class,
The decorated class, It doesn’t matter which implementation class is used to decorate it.
With the same business method, the decorated class calls the method of the decorating class to enhance the function of the decorating class

Example:

Class Diagram



##

public interface IReader {
	void read();
}
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public class Reader implements IReader {

	@Override
	public void read() {
		System.out.println("read of Reader");
	}

}
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public class BufferedReader implements IReader {
	
	private IReader mReader;
	public BufferedReader(IReader reader) {
		this.mReader = reader;
	}
	
	@Override
	public void read() {
		System.out.println("read of BufferedReader");
		mReader.read();
	}

}
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/*
 * 特点:
 * (1) 装饰对象和真实对象有相同的接口。这样客户端对象就能以和真实对象相同的方式和装饰对象交互。
 (2) 装饰对象包含一个真实对象的引用(reference)
 (3) 装饰对象接受所有来自客户端的请求。它把这些请求转发给真实的对象。
 (4) 装饰对象可以在转发这些请求以前或以后增加一些附加功能。这样就确保了在运行时,不用修改给定对象的结构就可以在外部增加附加的功能。
 在面向对象的设计中,通常是通过继承来实现对给定类的功能扩展。而装饰后,持有了真实对象,用以增强其功能。

 装饰者与适配器模式的区别
 关于新职责:适配器也可以在转换时增加新的职责,但主要目的不在此。装饰者模式主要是给被装饰者增加新职责的。
 关于其包裹的对象:适配器是知道被适配者的详细情况的(就是适配类)。装饰者只知道其接口是什么,
 至于其具体类型(是基类还是其他派生类)只有在运行期间才知道。
 
 */
public class Test {
	public static void main(String[] args) {
		Reader reader = new Reader();
		reader.read();
		System.out.println("----------");
		BufferedReader bufferedReader = new BufferedReader(reader);
		bufferedReader.read();

	}
}
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