在Java泛型参数列表中需要帮助<T>

Question

Hi guys i have a problem with this code:

//Class FileManip
public class FileManip{

private HTTPRequest<List<String>> addMe = new HTTPRequest<List<String>>();

    public void openFile(){

            try{
                BufferedReader buff = new BufferedReader(new FileReader("Saturday.txt"));
                try{
                    Double ctr = 0.0;
                    String readHTTPURIFromTxt = buff.readLine();
                    while (readHTTPURIFromTxt!=null){

                        if (!readHTTPURIFromTxt.isEmpty()){
                            addMe.putListHTTPCharTable(parseHTTPReqToCharbyChar(readHTTPURIFromTxt), ctr);
                            ctr++;
                        }
                    readHTTPURIFromTxt = buff.readLine();
                    }
                }

                finally{
                    buff.close();
                }   

            }
            catch(FileNotFoundException e){
                System.out.println("File not found"+e);
            }
            catch(IOException e){
                System.out.println("oist exception");
            }
        }

    public List<String> parseHTTPReqToCharbyChar(String getHTTP){ 
            List<String> parsingReq = new ArrayList<String>();
            String convChar=null;

                for (int x = 0; x<getHTTP.length(); x++){
                    convChar = Character.toString(getHTTP.charAt(x));
                    parsingReq.add(convChar);
                }

            return parsingReq;
        }
}


    //Class HTTPRequest
    public class HTTPRequest<T> {

    private LinkedHashMap<List<T>, Double> tableOfInitProbList = new LinkedHashMap<List<T>, Double>();

    public HTTPRequest(){
        }

    public HTTPRequest(List<T> entry, Double value){
            tableOfInitProbList.put(entry, value);
        }

    public void putListHTTPCharTable(List<T> uri, Double value){
            tableOfInitProbList.put(uri, value);
        }

    }

The problem is the line

addMe.putListHTTPCharTable(parseHTTPReqToCharbyChar(readHTTPURIFromTxt), ctr);

its in class filemanip openfile method inside the if statement. I wrote putListHttpCharTable to take 2 parameters List < T > and Double but whenever I pass the argument parseHTTPReqToCharbyChar(readHTTPURIFromTxt) which has a return type of List there is a compile time error. It reads

The method putListHTTPCharTable(List>, Double) in the type HTTPRequest> is not applicable for the arguments (List, Double)

I passed a method which has List < String > return type but somehow the compiler is trying to read it as List< List < T > > or a List < List < String > > instead of just being List < String >. Is there anyway to fix this?

Answer 1

Because :

HTTPRequest<List<String>>

means :

T <=> List<String> 

so the compiler sees this (for your "addMe" variable):

//Class HTTPRequest
    public class HTTPRequest<List<String>> {

    private LinkedHashMap<List<List<String>>, Double> tableOfInitProbList = new LinkedHashMap<List<List<String>>, Double>();

    public HTTPRequest(){
        }

    public HTTPRequest(List<List<String>> entry, Double value){
            tableOfInitProbList.put(entry, value);
        }

    public void putListHTTPCharTable(List<List<String>> uri, Double value){
            tableOfInitProbList.put(uri, value);
        }

    }

Answer 2

You are setting T to List<String>

Then the method is looking for a List<T> so you end up with List<List<String>>

This should work if you change your class to:

public class HTTPRequest<T> {

    private LinkedHashMap<T, Double> tableOfInitProbList = new LinkedHashMap<List<T>, Double>();

    public HTTPRequest(){
        }

    public HTTPRequest(T entry, Double value){
            tableOfInitProbList.put(entry, value);
        }

    public void putListHTTPCharTable(T uri, Double value){
            tableOfInitProbList.put(uri, value);
        }

}

Alternately, if you only want to specify type of list with your generic parameter this declaration should work:

private HTTPRequest<String> addMe = new HTTPRequest<String>();