[java] 왜 정적 메소드가 Java에서 추상적 일 수 없습니까?

이것은 끔찍한 언어 디자인이며 실제로 불가능한 이유는 없습니다.

실제로 다음은 JAVA 에서 수행 할 수 있는 방법에 대한 구현입니다 .

public class Main {

        public static void main(String[] args) {
                // This is done once in your application, usually at startup
                Request.setRequest(new RequestImplementationOther());

                Request.doSomething();
        }

        public static final class RequestImplementationDefault extends Request {
                @Override
                void doSomethingImpl() {
                        System.out.println("I am doing something AAAAAA");
                }
        }

        public static final class RequestImplementaionOther extends Request {
                @Override
                void doSomethingImpl() {
                        System.out.println("I am doing something BBBBBB");
                }
        }

        // Static methods in here can be overriden
        public static abstract class Request {

                abstract void doSomethingImpl();

                // Static method
                public static void doSomething() {
                        getRequest().doSomethingImpl();
                }

                private static Request request;
                private static Request getRequest() {
                        // If setRequest is never called prior, it will default to a default implementation. Of course you could ignore that too. 
                        if ( request == null ) {
                                return request = new RequestImplementationDefault();
                        }
                        return request;
                }
                public static Request setRequest(Request r){
                        return request = r;
                }

        }
}

================= 아래의 예 =================

getRequest를 찾으십시오. getRequestImpl … setInstance를 호출하여 호출하기 전에 구현을 변경할 수 있습니다.

import java.io.IOException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

/**
 * @author Mo. Joseph
 * @date 16 mar 2012
 **/

public abstract class Core {


    // ---------------------------------------------------------------        
    private static Core singleton; 
    private static Core getInstance() {
        if ( singleton == null )
            setInstance( new Core.CoreDefaultImpl() );  // See bottom for CoreDefaultImpl

        return singleton;
    }    

    public static void setInstance(Core core) {
        Core.singleton = core;
    }
    // ---------------------------------------------------------------        



    // Static public method
    public static HttpServletRequest getRequest() {      
        return getInstance().getRequestImpl();
    }


    // A new implementation would override this one and call setInstance above with that implementation instance
    protected abstract HttpServletRequest getRequestImpl();




    // ============================ CLASSES =================================

    // ======================================================================
    // == Two example implementations, to alter getRequest() call behaviour 
    // == getInstance() have to be called in all static methods for this to work
    // == static method getRequest is altered through implementation of getRequestImpl
    // ======================================================================

    /** Static inner class CoreDefaultImpl */
    public static class CoreDefaultImpl extends Core { 
        protected HttpServletRequest getRequestImpl() {
            return ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        }
    }

     /** Static inner class CoreTestImpl : Alternative implementation */
    public static class CoreTestImpl extends Core { 
        protected HttpServletRequest getRequestImpl() {
            return new MockedRequest();
        }
    }       

}

다음과 같이 사용됩니다 :

static {
     Core.setSingleton(new Core.CoreDefaultImpl());

     // Or

     Core.setSingleton(new Core.CoreTestImpl());

     // Later in the application you might use

     Core.getRequest(); 

}

답변