命令模式（Command）

命令模式

一. 命令模式

1.1 定义

• 对于“行为请求者”和“行为实现者”，将一组行为抽象为对象，实现二者的松耦合.

1.2 角色

• Command:抽象命令接口.
• ConcreteCommand:具体命令.
• Receiver:最终执行命令的对象.
• Invoker:命令对象的入口.

二. 具体实现

1.1 创建Command接口

    public interface ICommand {
        void execute();
    }

1.2 创建命令执行对象

    public class Receiver {
        public void execute(){
            System.out.println("receiver execute ... ");
        }
    }

1.3 创建具体Command实现类

    public class ConcreteCommandA implements ICommand {
        private Receiver receiver;
        public ConcreteCommandA(Receiver receiver){
            this.receiver = receiver;
        }
        @Override
        public void execute() {
            System.out.println("ConcreteCommandA execute ...");
            receiver.execute();
        }
    }
    public class ConcreteCommandB implements ICommand {
        private Receiver receiver;
        public ConcreteCommandB(Receiver receiver){
            this.receiver = receiver;
        }
        @Override
        public void execute() {
            System.out.println("ConcreteCommandB execute ...");
            receiver.execute();
        }
    }

1.4 创建命令入口

    public class Invoker {
        private ICommand concreteCommandA, concreteCommandB;
        public Invoker(ICommand concreteCommandA, ICommand concreteCommandB){
            this.concreteCommandA = concreteCommandA;
            this.concreteCommandB = concreteCommandB;
        }
        public void orderA(){
            concreteCommandA.execute();
        }
        public void orderB(){
            concreteCommandB.execute();
        }
    }

1.5 调用

    public static void main(String[] args) {
        Receiver receiver = new Receiver();
        Invoker invoker = new Invoker(new ConcreteCommandA(receiver), new ConcreteCommandB(receiver));
        invoker.orderA();
        invoker.orderB();
    }

1.6 输出

    ConcreteCommandA execute ...
    receiver execute ... 
    ConcreteCommandB execute ...
    receiver execute ... 

三. 优缺点

3.1 优点

• 降低耦合度.
• 新增一个命令/一组命令简单.
• 调用同一方法实现不同功能.

3.2 缺点

• 会产生过多具体命令类.

四. 源码

    https://github.com/Seasons20/DisignPattern.git

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