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();
    }
}