23命令模式Command

一、什么是命令模式

　　Command模式也叫命令模式 ，是行为设计模 式的一种。Command模式通过被称为 Command的类封装了对目标对象的调用行为以及调用参数。

二、命令模式的应用场景

　　在面向对象的程序设计中，一个对象调用另一个对象， 一般情况下的调用过程是：创建目标对象实例；设置调 用参数；调用目标对象的方法。

　　但在有些情况下有必要使用一个专门的类对这种调用 过程加以封装，我们把这种专门的类称作command类。

　　　　- 整个调用过程比较繁杂，或者存在多处这种调用。 这时，使用Command类对该调用加以封装，便于功能的 再利用。

　　　　- 调用前后需要对调用参数进行某些处理。

　　　　- 调用前后需要进行某些额外处理，比如日志，缓存，记录历史操作等。

三、命令模式的结构

四、命令模式的角色和职责

　　Command    Command抽象类。

　　ConcreteCommand    Command的具体实现类。

　　Receiver    需要被调用的目标对象。

　　Invorker    通过Invorker执行Command对象。

ex1：

小商贩

 /*
  * 小商贩
  */
 public class Peddler {

     //卖苹果
     public void sailApple() {
         System.out.println("卖苹果");
     }

     //卖香蕉
     public void sailBanana() {
         System.out.println("卖香蕉");
     }
 }

测试

 public class MainClass {
     public static void main(String[] args) {
         Peddler peddler = new Peddler();
         peddler.sailApple();
         peddler.sailBanana();
     }
 }

================================================================================

ex2:

小商贩

 /*
  * 小商贩
  */
 public class Peddler {

     //卖苹果
     public void sailApple() {
         System.out.println("卖苹果");
     }

     //卖香蕉
     public void sailBanana() {
         System.out.println("卖香蕉");
     }
 }

命令

 //命令
 public abstract class Command {
     private Peddler peddler;

     public Command(Peddler peddler) {
         this.peddler = peddler;
     }

     public Peddler getPeddler() {
         return peddler;
     }

     public void setPeddler(Peddler peddler) {
         this.peddler = peddler;
     }

     public abstract void sail();
 }

苹果命令

 //苹果命令
 public class AppleCommand extends Command {

     public AppleCommand(Peddler peddler) {
         super(peddler);
     }

     public void sail() {
         this.getPeddler().sailApple();
     }
 }

香蕉命令

 //香蕉命令
 public class BananaCommand extends Command{

     public BananaCommand(Peddler peddler) {
         super(peddler);
     }

     public void sail() {
         this.getPeddler().sailBanana();
     }
 }

测试

 public class MainClass {
     public static void main(String[] args) {
         Peddler peddler = new Peddler();
 //        peddler.sailApple();
 //        peddler.sailBanana();

         Command appleCommand = new AppleCommand(peddler);
         Command bananaCommand = new BananaCommand(peddler);
         appleCommand.sail();
         bananaCommand.sail();
     }
 }

=====================================================

ex3：

小商贩

 /*
  * 小商贩
  */
 public class Peddler {

     //卖苹果
     public void sailApple() {
         System.out.println("卖苹果");
     }

     //卖香蕉
     public void sailBanana() {
         System.out.println("卖香蕉");
     }
 }

命令　　抽象

 //命令
 public abstract class Command {
     private Peddler peddler;

     public Command(Peddler peddler) {
         this.peddler = peddler;
     }

     public Peddler getPeddler() {
         return peddler;
     }

     public void setPeddler(Peddler peddler) {
         this.peddler = peddler;
     }

     public abstract void sail();
 }

苹果命令

 //苹果命令
 public class AppleCommand extends Command {

     public AppleCommand(Peddler peddler) {
         super(peddler);
     }

     public void sail() {
         this.getPeddler().sailApple();
     }
 }

香蕉命令

 package com.ibeifemg.ex3;
 //香蕉命令
 public class AppleCommand extends Command {

     public AppleCommand(Peddler peddler) {
         super(peddler);
     }

     public void sail() {
         this.getPeddler().sailApple();
     }
 }

服务

 //服务
 public class Waiter {
     private Command command;

     public Command getCommand() {
         return command;
     }

     public void setCommand(Command command) {
         this.command = command;
     }

     public void sail() {
         command.sail();
     }
 }

测试

 public class MainClass {
     public static void main(String[] args) {
         Peddler peddler = new Peddler();
 //        peddler.sailApple();
 //        peddler.sailBanana();

         Command appleCommand = new AppleCommand(peddler);
         Command bananaCommand = new BananaCommand(peddler);
 //        appleCommand.sail();
 //        bananaCommand.sail();
         Waiter waiter = new Waiter();
         waiter.setCommand(appleCommand);
         waiter.sail();
         waiter.setCommand(bananaCommand);
         waiter.sail();
     }
 }

========================================================================

ex4：

小商贩

 /*
  * 小商贩
  */
 public class Peddler {

     //卖苹果
     public void sailApple() {
         System.out.println("卖苹果");
     }

     //卖香蕉
     public void sailBanana() {
         System.out.println("卖香蕉");
     }
 }

命令

 //命令
 public abstract class Command {
     private Peddler peddler;

     public Command(Peddler peddler) {
         this.peddler = peddler;
     }

     public Peddler getPeddler() {
         return peddler;
     }

     public void setPeddler(Peddler peddler) {
         this.peddler = peddler;
     }

     public abstract void sail();
 }

苹果命令

 //苹果命令
 public class AppleCommand extends Command {

     public AppleCommand(Peddler peddler) {
         super(peddler);
     }

     public void sail() {
         this.getPeddler().sailApple();
     }
 }

香蕉命令

 //香蕉命令
 public class BananaCommand extends Command{

     public BananaCommand(Peddler peddler) {
         super(peddler);
     }

     public void sail() {
         this.getPeddler().sailBanana();
     }
 }

服务

 //服务
 public class Waiter {
     private List<Command> commands = new ArrayList<Command>();

     public void setOrder(Command command) {
         commands.add(command);
     }

     public void removeOrder(Command command) {
         commands.remove(command);
     }

     public void sail() {
         for(Command command : commands) {
             command.sail();
         }
     }
 }

测试

 public class MainClass {
     public static void main(String[] args) {
         Peddler peddler = new Peddler();
 //        peddler.sailApple();
 //        peddler.sailBanana();

         Command appleCommand = new AppleCommand(peddler);
         Command bananaCommand = new BananaCommand(peddler);
 //        appleCommand.sail();
 //        bananaCommand.sail();
         Waiter waiter = new Waiter();

         //下订单
         waiter.setOrder(appleCommand);
         waiter.setOrder(bananaCommand);

         //移除订单某项
         waiter.removeOrder(appleCommand);

         waiter.sail();
     }
 }