装饰（Decorator）模式又名包装（Wrapper）模式[GOF95]。装饰模式以对客户端透明的方式扩展对象的功能，是继承关系的一个代替方案。

//抽象构件(Component)
public interface Component
{
    void sampleOperation();
}
//具体构件(Concrete Component)
public class ConcreteComponent implements Component
{
    public void sampleOperation()
    {
        // Write your code here
    }
}
//装饰(Decorator)
public class Decorator implements Component
{
 public Decorator(Component component)
    {
//        super();
        this.component = component;
    }

    public Decorator() {
    }

    public void sampleOperation()
    {
        component.sampleOperation();
    }
    private Component component;
}
//具体装饰(Concrete Decorator)
public class ConcreteDecorator extends Decorator
{
    public void sampleOperation()
    {
        super.sampleOperation();
    }
}

一个用Java语言实现的Grep系统

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.FilterReader;

public class GrepReader extends FilterReader
{
    protected String substring;     // substring to be matched
    protected BufferedReader in; // InputReader

    public GrepReader( FileReader in, String substring )
    {
        super( in );
        this.in = new BufferedReader( in );
        this.substring = substring;
        lineNumber = 0;
    }

    public final String readLine( ) throws IOException
    {
        String line;
        // step forward until line matching substring
        do
        {
            line = in.readLine( ); lineNumber++;
        } while ( (line != null) && line.indexOf( substring ) == -1 );
        return line;
    }

 private int lineNumber;
 
 public int lineNo( ) { return lineNumber; }
  
} // class GrepReader

import java.io.PrintStream;

public class GrepView
{
    PrintStream out ;
  public GrepView()
  {
  out = System.out;
 }

 public void println(String line)
    {
      out.println(line);
    }
}

import java.io.*;

/** This class implements a subset of the UNIX tool grep and
 ** demonstrates the use of the GrepInputStream class.
 ** It prints the filename, linenumbers and lines of the file that
 ** contains a specified substring (no regexp)
 ** @see GrepInputStream
 ** @author Ulrik Schroeder
 ** @version Joop97-Demo
 **/
public class Grep {
 static GrepReader g;  // own FilterReader definition

    private static GrepView gv = new GrepView();
 /** reads substring and files to be looked through from commandline.
  ** Unfortunately DOS shell does not expand wildcards when calling Grep.
  ** @param args command line arguments: 1 substring, 2 .. n Filenames
  ** @see <{DataInputStream}>
  ** @see GrepInputStream
  ** @see GrepInputStream#GrepInputStream
  ** @see GrepInputStream#line
  ** @see GrepInputStream#lineNo
  **/
 public static void main( String[] args  )
    {
 
        if ( args.length <= 1 )
        {
            gv.println("Usage: java Grep ");
            gv.println("       no regexp");
            gv.println("       files to be searched in");
            System.exit( 1 );
        }
       
  String line;
        try
        {
            gv.println( "\nGrep: 搜索 " + args[0] + " 文件 " + args[1] );
            gv.println( "文件行号\t\t 下面的行里含有所搜索的字符串\n" );
//    gv.println( "\n--> Grep: searching " + args[ 0 ] + " in " + args[ i ] + " <----------" );
//   gv.println( "File:Line:\t Line containing substring\n" );
   g = new GrepReader( new FileReader( args[1] ), args[0] );
   for( ; ; )
               {
    line = g.readLine( );
    if (line == null) break;
    gv.println( args[1] + g.lineNo( ) + ":\t" + line );
   } // loop through lines of file
   g.close( );
        } // try
  catch ( IOException e ) {
   gv.println( e.getMessage() );
  } // catch IOException
    }

}

一个例子：发票系统

package com.javapatterns.decorator.printinvoice;

import java.util.Date;
import java.util.Vector;
import java.text.NumberFormat;

abstract public class Order
{
    /**
     * @link aggregation
     * @directed
     * @supplierCardinality 0..*
     * @clientCardinality 1
     */
    private OrderLine lnkOrderLine;
    protected String customerName;
    protected Date salesDate;
 protected Vector items = new Vector(10);

    public void print()
    {
  for (int i = 0 ; i < items.size() ; i++)
        {
   OrderLine item = (OrderLine) items.get(i);
            item.printLine();
        }
    }

    public String getCustomerName()
    {
        return customerName;
    }

    public void setCustomerName(String customerName)
    {
        this.customerName = customerName;
    }

    public Date getSalesDate()
    {
        return salesDate;
    }

    public void setSalesDate(Date salesDate)
    {
        this.salesDate = salesDate;
    }

    public void addItem(OrderLine item)
    {
        items.add(item);
    }

    public void remoteItem(OrderLine item)
    {
        items.remove(item);
    }

    public double getGrandTotal()
    {
        double amnt = 0.0D;

  for (int i = 0 ; i < items.size() ; i++)
        {
   OrderLine item = (OrderLine) items.get(i);
            amnt += item.getSubtotal();
        }

        return amnt;
    }

    protected String formatCurrency(double amnt)
    {
        return NumberFormat.getCurrencyInstance().format(amnt);
    }

}

package com.javapatterns.decorator.printinvoice;

public class SalesOrder extends Order
{
    public SalesOrder() {
    }

    public void print()
    {
        super.print();
    }
}

package com.javapatterns.decorator.printinvoice;

abstract public class OrderDecorator extends Order
{
    /**
     * @link aggregation
     * @directed
     * @supplierCardinality 1
     * @clientCardinality 0..1
     */
    protected Order order;

    public OrderDecorator(Order order)
    {
        this.order = order;
        this.setSalesDate( order.getSalesDate() );
        this.setCustomerName( order.getCustomerName() );
    }

    public void print()
    {
  super.print();
    }
}

package com.javapatterns.decorator.printinvoice;

public class HeaderDecorator extends OrderDecorator
{
    public HeaderDecorator(Order anOrder)
    {
        super(anOrder);
    }

    public void print()
    {
        this.printHeader();
        super.order.print();
    }

    private void printHeader()
    {
        System.out.println("\t***\tI N V O I C E\t***\nXYZ Incorporated\nDate of Sale: "
            + order.getSalesDate());
        System.out.println("========================================================");
        System.out.println("Item\t\tUnits\tUnit Price\tSubtotal");
    }
}

package com.javapatterns.decorator.printinvoice;

import java.text.NumberFormat;

public class FooterDecorator extends OrderDecorator
{
    public FooterDecorator(Order anOrder)
    {
        super(anOrder);
    }

    public void print()
    {
        super.order.print();
        printFooter();
    }

    private void printFooter()
    {

        System.out.println("========================================================");
        System.out.println("Total\t\t\t\t" +
            formatCurrency(super.order.getGrandTotal()));
    }

}

package com.javapatterns.decorator.printinvoice;

import java.text.NumberFormat;

public class OrderLine
{
    private String itemName;
    private int units;
    private double unitPrice;

    public String getItemName()
    {
        return itemName;
    }

    public void setItemName(String itemName)
    {
        this.itemName = itemName;
    }

    public int getUnits()
    {
        return units;
    }

    public void setUnits(int units)
    {
        this.units = units;
    }

    public double getUnitPrice()
    {
        return unitPrice;
    }

    public void setUnitPrice(double unitPrice)
    {
        this.unitPrice = unitPrice;
    }

    public void printLine()
    {
  System.out.println(itemName + "\t" + units
            + "\t" + formatCurrency(unitPrice)
            + "\t" + formatCurrency(getSubtotal()));
    }

    public double getSubtotal()
    {
        return unitPrice * units;
    }

    private String formatCurrency(double amnt)
    {
        return NumberFormat.getCurrencyInstance().format(amnt);
    }
}

package com.javapatterns.decorator.printinvoice;

import java.util.Date;

public class Client {
    /**
     * @directed
     */
    private static Order order;

    public static void main(String[] args)
    {
        rder = new SalesOrder();
  order.setSalesDate(new Date());
        order.setCustomerName("XYZ Repair Shop");

        OrderLine line1 = new OrderLine();

        line1.setItemName("FireWheel Tire");
        line1.setUnitPrice(154.23);
        line1.setUnits(4);

        order.addItem(line1);

        OrderLine line2 = new OrderLine();

        line2.setItemName("Front Fender");
        line2.setUnitPrice(300.45);
        line2.setUnits(1);

        order.addItem(line2);

        rder = new HeaderDecorator(new FooterDecorator(order));

        order.print();
    }
}