다형성 & Upcasting & Downcasting

출처

https://opentutorials.org/course/1223/6127

https://kdyang.tistory.com/16

Spring 프로젝트에서
<컨트롤러>
@Controller
public class WelcomeWebController {
	@Resource(name = "welcomeWebService") // @Resource : 인스턴스를 생성해준다고 보면 됌
	private WelcomeWebService welcomeWebService;
	@RequestMapping(value = "welcomeWebMap.do")
	public String welcomeWebMap(HttpServletRequest request, ModelMap model) throws Exception {
		HashMap<String, Object> resMap = new HashMap<String, Object>();
		
		resMap.put("age", request.getParameter("age"));
		
		List<EgovMap> welcomeWebList = welcomeWebService.selectWelcomeWebMapList(resMap);
		
		model.addAttribute("welcomeWebList", welcomeWebList);
		
		return "welcomeWeb/welcomeWeb.tiles";
	}
}
<서비스>
public interface WelcomeWebService {
	List<EgovMap> selectWelcomeWebServiceList() throws Exception;
	List<EgovMap> selectWelcomeWebMapList(HashMap<String, Object> resMap) throws Exception;
}
<서비스 임플>
@Service("welcomeWebService") // 해당 클래스가 Service라는 것을 알리기 위한 Annotation
public class WelcomeWebServiceImpl implements WelcomeWebService {
	@Resource(name = "welcomeWebMapper")
	private WelcomeWebMapper welcomeWebMapper;
	@Override
	public List<EgovMap> selectWelcomeWebServiceList() throws Exception {
		return welcomeWebMapper.selectWelcomeWebServiceList();
	}
	@Override
	public List<EgovMap> selectWelcomeWebMapList(HashMap<String, Object> resMap) throws Exception {
		return welcomeWebMapper.selectWelcomeWebMapList(resMap);
	}
}
WelcomeWebService welcomeWebService = new WelcomeWebServiceImpl(); => WelcomeWebServiceImpl의 데이터 타입으로 
인터페이스 WelcomeWebService를 지정            
welcomeWebService.selectWelcomeWebMapList(resMap); => WelcomeWebServiceImpl의 selectWelcomeWebMapList 메소드를 오버라이딩