《Java与模式》一书的源代码

				package com.javapatterns.command.document;
				
				public class Invoker
				{
				    private Command command;
				
				    public Invoker(Command cmd)
				    {
				        command = cmd;
				    }
				
				    public void invoke()
				    {
				        if (command != null)
				        {
				            command.execute();
				        }
				    }
				}