设计模式之命令模式

命令模式

1. 命令模式结构图：

   

2. 示例代码：

   // 命令接受者，负责具体执行命令
   public class Receiver {
   
       public void action(){
           System.out.println("开始执行命令＝＝＝＝＝＝＝＝");
       }
   }
   
   // 命令抽象类
   public interface Command {
       void execute();
   }
   
   // 具体命令角色Ａ
   public class ConcreteCommandA implements Command{
   
       private Receiver receiver;
   
       public ConcreteCommandA(Receiver receiver) {
           this.receiver = receiver;
       }
   
       @Override
       public void execute() {
           System.out.println("执行命令Ａ");
           receiver.action();
       }
   }
   
   // 具体命令角色Ｂ
   public class ConcreteCommandB implements Command{
   
       private Receiver receiver;
   
       public ConcreteCommandB(Receiver receiver) {
           this.receiver = receiver;
       }
   
       @Override
       public void execute() {
           System.out.println("执行命令Ｂ");
           receiver.action();
       }
   }
   
   // 命令请求者
   public class Invoker {
       List<Command> list = new ArrayList<>();
   
       public void attach(Command command){
           System.out.println("添加命令");
           list.add(command);
       }
   
       public void detach(){
        System.out.println("撤销命令");
        if (!list.isEmpty()){
            list.remove(list.size() -1);
        }
      }
   
       public void execute(){
           list.forEach(a -> a.execute());
       }
   }
   
   // 测试类
   public class CommandTest {
   
       public static void main(String[] args) {
           Invoker invoker = new Invoker();
           invoker.attach(new ConcreteCommandA(new Receiver()));
           invoker.attach(new ConcreteCommandA(new Receiver()));
           invoker.attach(new ConcreteCommandB(new Receiver()));
           invoker.attach(new ConcreteCommandB(new Receiver()));
           invoker.execute();
       }
   }
   
   

3. 总结：

   优点：通过引入抽象接口，解偶了命令请求与实现，扩展性好，支持组合命令，可在现有命令的基础上，增加额外的功能；

   缺点：具体命令类可能过多，增加了系统的复杂性．