[week04] Command pattern

1. Command Pattern

2. Given Hardware & Our Vendor Classes

3. Without Using Command Pattern

4. Implementing Command interface

5. Our Approach

6. Collaborations

7. Extending the Remote Control

8. After Setting the Commands

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1. Command Pattern

목적

• Request를 객체로 인캡슐화하자
• 각 command 객체는 execute 또는 undo 메서드만 노출함
• Request가 queuing과 callback과 같은 relationships에 근거해 전형적인 객체로 다루어짐

 

Use when?

• Requests가 다양한 시간에 다양한 순서로 명세되고, 큐에 보관되고, 실행될 필요가 있을 때
• Requests의 기록(history)이 필요할 때
• invoker가 invocation을 다루는 객체로부터 분리되어야할 때

 

 

2. Given HardWare & Our Vendor Classes

여러 서비스들이 합쳐진 리모트 컨트롤

 

 

3. Without Using Command Pattern

  이런 식으로 코드 짜면, button 행동을 수정하고 싶을때마다 client code에 손을 대야 함

if(command == Slot1On)
	light.on();
else if(command== Slot1Off)
	light.off();

 

 

4. Implementing Command interface

// Command interface
public interface Command{
	public void execute();
    //public void undo();
}

public class LightOnCommand implements Command{
	Light light; // Stores info. about its receiver
    
    public LightOnCommand(Light light){
    	this.light = light;
    }
    
    public void execute(){
    	light.on();
    }
}

public class LightOffCommand implements Command{
	Light light;
    public LightOffCommand(Light light){
    	this.light = light;
    }
    public void execute(){
    	light.off();
    }
}

// Using the command object (Building Invoker)
public class SimpleRemoteControl{
	Command slot;
    
    public SimpleRemoteControl(){ }
    
    public void setcommand(Command command){
    	slot = command;
    }
    
    public void buttonWaspressed(){
    	slot.execute();
    }
}

// Client Program
public class RemoteControlTest{
	public static void main(String[] args){
    	SimpleRemoteControl remote = new SimpleRemoteControl();
        Light light = new light();
        LightOnCommand lightOn = new LightOnCommand(light);
        remote.setCommand(lightOn);
        remote.buttonWasPressed();
    }
}

 

 

5. Our Approach

1) Client

• client는 command 객체를 만들 수 있음
• command 객체는 receiver의 action 집합으로 구성됨

 

2) Command

• action들과 Receiver는 command 객체에 함께 붙어 있음
• command 객체는 execute() 메서드를 제공함
• execute() 메서드는 action들을 인캡슐화하고, Receiver의 action들을 일으키기 위해 호출됨

 

3) Invoker

• client는 Invoker 객체의 setCommand() 메서드를 호출해, Invoker 객체로 command 객체를 넘긴다.
• 어느 시점에, Invoker는 command 객체의 execute() 메서드를 호출한다.

 

4) Receiver

• Receiver의 action들을 결과로 함

 

 

request를 객체로 인캡슐화 해라.

그러면, clients와 다양한 requests, queue, log requests 등을 파라미터화하고, 실을 수 없는(unloadable) operations을 지원해라.

 

 

6. Collaborations

 

 

7. Extending the Remote Control

public class RemoteControl{

	Command[] oncommands;
    Command[] offcommands;
    
    RemoteControl(){
    	oncommands = new Command[7];
        offcommands = new Command[7];
        
        Command noCommand = new NoCommand();
        for(int i=0; i<7; i++){
        	onCommand[i] = noCommand;
            offCommand[i] = noCommand;
        }
    }
}

public class NoCommand implements Command{
	public void execute(){}
}

public void setCommand(int slot, Command oncommand, Command offcommand){
	oncommand[slot] = oncommand;
    offcommand[slot] = offcommand;
}

public void onButtonWasPushed(int slot){
	oncommand[slot].execute();
}

public void offButtonWasPushed(int slot){
	ffncommand[slot].execute();
}

//Client Program
public class RemoteLoader{
	public static void main(String[] args){
    	// create invoker
        RemoteControl remotecontrol = new RemoteControl();
        
        // create receivers
        Light livingRoomLight = new Light("Living Room");
        Light kitchenLight = new Light("Kitchen");
        
        // create commands
        Command livingRoomLightOn = new LightOnCommand(livingRoomLight);
        Command livingRoomLightOff = new LightOffCommand(livingRoomLight);
        Command kitchenlightOn = new LightOnCommand(kitchenLight);
        Command kitchenlightOff = new LightOffCommand(kitchenLight);
    
    	// linking the invoker with the commands
        remotecontrol.setCommand(0, livingRoomLightOn, livingRoomLightOff);
        remotecontrol.setCommand(1, kitchenlightOn, kitchenlightOff);
        remotecontrol.onButtonWasPushed(0);
        remotecontrol.offButtonWasPushed(0);
        remotecontrol.onButtonWasPushed(1);
        remotecontrol.offButtonWasPushed(1);
    }
}

 

 

8. After Setting the Commands