22-04-11-비지터패턴-2부-패턴적용하기

01.비지터패턴 적용하기

01.1 Shape.java

• before

• public interface Shape {
      void printTo(Device device);
  }// 모든 디바이스에 쓰기 위함

• after

• public interface Shape {
      void printTo(Phone phone);
      void printTo(Watch watch);
  }

01.2 Circle.java

• before

• public class Circle implements Shape{
  	@Override
      public void printTo(Device device){
          if(device instanceof Phone){
              System.out.println("print Circle to Phone");
          }else if(device instanceof Watch){
              System.out.println("print Circle to Watch");
          }
      }
  }

• after

• public class Circle implements Shape{
  	@Override
      public void printTo(Phone phone){
          System.out.println("print Circle to Phone");
      }
      @Override
      public void printTo(Watch watch){
          System.out.println("print Circle to Watch");
      }
  }

01.3 Retangle.java

• before

• public class Rectangle implements Shape{
  	@Override
      public void printTo(Device device){
          if(device instanceof Phone){
              System.out.println("print Rectangle to Phone");
          }else if(device instanceof Watch){
              System.out.println("print Rectangle to Watch");
          }
      }
  }

• after

• public class Rectangle implements Shape{
  	@Override
      public void printTo(Phone phone){
          System.out.println("print Rectangle to Phone");
      }
      @Override
      public void printTo(Watch watch){
          System.out.println("print Rectangle to Watch");
      }
  }

01.4 Triangle.java

• before

• public class Triangle implements Shape{
  	@Override
      public void printTo(Device device){
          if(device instanceof Phone){
              System.out.println("print Triangle to Phone");
          }else if(device instanceof Watch){
              System.out.println("print Triangle to Watch");
          }
      }
  }

• after

• public class Triangle implements Shape{
  	@Override
      public void printTo(Phone phone){
          System.out.println("print Triangle to Phone");
      }
      @Override
      public void printTo(Watch watch){
          System.out.println("print Triangle to Watch");
      }
  }

01.5 Client.java

• before
  • 위의 클라이언트 코드로 하면 에러가 생기는 이유?
    • Device device 이것이 아무리 폰과 워치의 상위 타입이라고 하더라도
      • 컴파일 타임에서 어떤 타입이될지 모름
      • 런타임 중에 메소드 오버라이딩는 찾을 수 없음
        • 스태틱한 매핑을 해버림
    • 메소드 오버라이딩은 컴파일 타임에 됨

• public class Client{
      public static void main(String[] args)
      {
          Shape rectangle = new Rectangle();
          Device device = new Phone();
          rectangle.printTo(device);
  	}
  }

• after

• public class Client{
      public static void main(String[] args)
      {
          Shape rectangle = new Rectangle();
          rectangle.printTo(new Phone());
  	}
  }

02.제대로 동작하게 패턴 적용

02.1 Shape.java

• before

• public interface Shape {
      void printTo(Phone phone);
      void printTo(Watch watch);
  }

• after

• public interface Shape {
      void accept(Device device);
  }

02.2 Circle.java

• before

• public class Circle implements Shape{
  	@Override
      public void printTo(Phone phone){
          System.out.println("print Circle to Phone");
      }
      @Override
      public void printTo(Watch watch){
          System.out.println("print Circle to Watch");
      }
  }

• after

• public class Circle implements Shape{
  	@Override
  	public void accept(Device device){
  		device.print(this);
      }
  }

02.3 Retangle.java

• before

• public class Rectangle implements Shape{
  	@Override
      public void printTo(Phone phone){
          System.out.println("print Rectangle to Phone");
      }
      @Override
      public void printTo(Watch watch){
          System.out.println("print Rectangle to Watch");
      }
  }

• after

• public class Rectangle implements Shape{
  	@Override
  	public void accept(Device device){
  		device.print(this);
      }
  }

02.4 Triangle.java

• before

• public class Triangle implements Shape{
  	@Override
      public void printTo(Phone phone){
          System.out.println("print Triangle to Phone");
      }
      @Override
      public void printTo(Watch watch){
          System.out.println("print Triangle to Watch");
      }
  }

• after

• public class Triangle implements Shape{
  	@Override
  	public void accept(Device device){
  		device.print(this);
      }
  }

02.5 Device.java

public interface Device{
    void print(Circle circle);
    void print(Retangle retangle);
    void print(Triangle triangle);
}

02.6 Phone.java

• before

• public Phone implements Device{
  }

• after

• public Phone implements Device{
      @Override
      public void print(Circle circle){
  		System.out.println("Print Circle to Phone");
      }
      
      @Override
      public void print(Retangle retangle){
  		System.out.println("Print Retangle to Phone");
      }
      
      @Override
      public void print(Triangle triangle){
  		System.out.println("Print Triangle to Phone");
      }    
  }

02.7 Watch.java

• before

• public Watch implements Device{
  }

• after

• public Watch implements Device{
      @Override
      public void print(Circle circle){
  		System.out.println("Print Circle to Watch");
      }
      
      @Override
      public void print(Retangle retangle){
  		System.out.println("Print Retangle to Watch");
      }
      
      @Override
      public void print(Triangle triangle){
  		System.out.println("Print Triangle to Watch");
      }    
  }

02.8 Client.java

• before

• public class Client{
      public static void main(String[] args)
      {
          Shape rectangle = new Rectangle();
          Device device = new Phone();
          rectangle.printTo(device);
  	}
  }

• after

• public class Client{
      public static void main(String[] args)
      {
          Shape rectangle = new Rectangle();
          Device device = new Phone();
          rectangle.accept(device);
  	}
  }

03.왜 더블 디스패치라고 하는가?

• rectangle.accept(device);
  • 여기서 어떤 accept로 찾아가야하는지에 대한 디스패치가 일어남
• device.print(this);
  • 어떤 디바이스의 print를 써야하는지에 대해서 런타임에서 알아서 또 찾아서 디스패치가 일어남

https://3dpit.github.io/posts/%EB%B9%84%EC%A7%80%ED%84%B0%ED%8C%A8%ED%84%B4-2%EB%B6%80-%ED%8C%A8%ED%84%B4%EC%A0%81%EC%9A%A9%ED%95%98%EA%B8%B0/

22-04-11-비지터패턴-2부-패턴적용하기