命令模式

命令模式的定义：
Encapsulated a request as an object ,thereby letting you parameterize clients with different requests, queue or log requests,
and support undoable operations.
将一个请求封装成一个对象，从而让你使用不同的请求把客户端参数化，对请求排队或者记录请求日志，可以提供命令的撤销和恢复功能

在类图中有三个角色：
Receive接收者角色:该角色就是执行角色，命令传递到这里就会被执行
Command命令角色：需要执行的所有命令都在这里声明
Invoker调用者角色：接收到命令，并执行命令

命令模式是把请求方(Invoker)和执行方(Receiver)分开
//通用Receiver类
public abstract class Receiver{
    public abstract void doSomething();
}
//具体Receiver类
public class ConcreteReceiver1 extends Receiver{
    public void doSomething(){...}
}

public class ConcreteReciver2 extends Receiver{
    public void doSomething(){...}
}

//抽象Command类
public abstract class Command{
    public abstract void execute();
}
//具体Command类
public class ConcreteCommand1 extends Command{
    private Receiver receiver;
    public ConcreteCommand1(Receiver receiver){
        this.receiver=receiver;
    }
    
    public void execute(){
        this.receiver.doSomething();
    }
    
}
public class ConcreteCommand2 extends Command{
    private Receiver receiver;
    public ConcreteCommand2(Receiver receiver){
        this.receiver=receiver;
    }
    
    public void execute(){
        this.receiver.doSomething();
    }    
}

public class Invoker{
    private Command command;
    public void setCommand(Command _command){
        this.command=_command;
    }
    public void action(){
        this.command.execute();
    }
}

public class Client{
    public static void main(String[] args){    
        Invoker invoker=new Invoker();
        Receiver receiver=new ConcreteReceiver1();
        Command command=new ConcreteCommand1(receiver);
        invoker.setCommand(command);
        invoker.action();
    }
}