Re: cannot find symbol?

From:

Daniel Pitts <newsgroup.nospam@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 04 May 2013 18:07:56 -0700

Message-ID:

<Nhiht.63227$2b6.41114@newsfe10.iad>

On 5/4/13 1:58 PM, qwertmonkey@syberianoutpost.ru wrote:

  this is what I had in mind. The thing is that I wanted to get a typed object
~
  public T_Ctxt getCtxtDTO();
~
  instead of a flat one
~
  public Object getCtxtDTO();
~
  and even though I haven't had the chance/need to learn about generics and how
they relate to reflection I have the (probably wrong) hunch that there should
be a way to do that

Reflection is usually bad. There are places for it, but if you can solve
your problem without it, then do so.

getCtxtDTO will return an Object of the static type T_Ctxt, but T_Ctxt
has no information about it, other than it extends Object. In order to
know more about it, you need an interface or base-class.

class Foo<T_Ctxt> in Java is *not* the same as in C++. Templates are not
even closely possible in Java. I will say it one last time. You need to
use an interface.

Perhaps you should read about Generics, since that is what you're trying
(and failing) to use. A great introduction is here:

http://docs.oracle.com/javase/tutorial/extra/generics/

Read that, and one of your problems will be solved.

~
  lbrtchx
~
// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

import java.util.Date;

import java.io.IOException;

import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

// __
class IADObj{
  private double d;
  private String aS;
  private Date Dt;
// __
  IADObj(){}
// __
  public void setCtxt(String[] aSAr){
   this.d = (new Double(aSAr[0])).doubleValue();
   this.aS = aSAr[1];
   this.Dt = new Date((new Long(aSAr[2])).longValue());
  }
// __
  public String toString(){ return(" d: |" + d + "|, aS: |" + aS + "|, Dt: |" +
Dt + "|"); }
}

// __
class Ho3K{
  private String aS;
  Ho3K(){}
  public void setCtxt(String[] aSAr){ this.aS = aSAr[0]; }
  public String toString(){ return(" aS: |" + aS + "|"); }
}

// __
interface verifiableCLIContext12<T_Ctxt>{
  public boolean verifyCtxt(String[] aSArs, Class<? extends T_Ctxt> TpArgK);
// public T_Ctxt getCtxtDTO();
  public Object getCtxtDTO();
}

// __
class DTO_T_Ctxt12<T_Ctxt> implements verifiableCLIContext12<T_Ctxt> {
// private T_Ctxt tCtxt; // operating context

  private Object OCtxtObj; // operating context

  private final Class[] KParams = new Class[]{String[].class};

// __
  DTO_T_Ctxt12(){ System.err.println("// __ object created: |" + getTimeStamp() + "|"); }

// __
  private String getTimeStamp(){ return((new Date()).toString()); }

// __
  public boolean verifyCtxt(String[] aSAr, Class<? extends T_Ctxt> TpArgK){
   int iArSz= Integer.MIN_VALUE;
   boolean Is = ((aSAr != null) && ((iArSz = aSAr.length) > 0));
   if(Is){
    for(int i = 0; (i < iArSz); ++i){
     System.err.println("// __ aSAr[" + i + "]: |" + aSAr[i] + "|");
    }
// __
    try{
     OCtxtObj = (T_Ctxt)TpArgK.newInstance();
     Method VerMthd = (OCtxtObj.getClass()).getDeclaredMethod("setCtxt", KParams);
     VerMthd.invoke(OCtxtObj, new Object[]{aSAr});
System.err.println("// __ |" + this.getClass() + "." +
Thread.currentThread().getStackTrace()[1].getMethodName() + "|" + OCtxtObj + "|");
    }catch(InstantiationException InstX){ InstX.printStackTrace(System.err); }
     catch(IllegalAccessException IlglAxX){ IlglAxX.printStackTrace(System.err); }
     catch(NoSuchMethodException NMthddX){ NMthddX.printStackTrace(System.err); }
     catch(InvocationTargetException InvkTrgtX){ InvkTrgtX.printStackTrace(System.err); }

   }// (Is)
// __
   return(Is);
  }

// __
  public Object getCtxtDTO(){
System.err.println("// __ |" + this.getClass() + "." +
Thread.currentThread().getStackTrace()[1].getMethodName() + "|");
   return(OCtxtObj);
  }
}

// __
public class DTO_T_Ctxt12Test{
  public static void main(String[] args) {
   String[] aSAr;
   Object RObj;
// __
   System.err.println("// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ");
   IADObj IAD = new IADObj();
   aSAr = new String[]{"37", "abc",
  (new Long(System.currentTimeMillis())).toString()};
   DTO_T_Ctxt12<IADObj> DTO_IADObj = new DTO_T_Ctxt12<IADObj>();

   DTO_IADObj.verifyCtxt(aSAr, IAD.getClass());
   RObj = DTO_IADObj.getCtxtDTO();
   System.err.println("// __ |" + RObj.getClass() + "|" + RObj + "|");
// __
   System.err.println("// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ");
   Ho3K Ho3 = new Ho3K();
   aSAr = new String[]{"Ho, ho, ho!"};
   DTO_T_Ctxt12<Ho3K> DTO_Ho3 = new DTO_T_Ctxt12<Ho3K>();

   DTO_Ho3.verifyCtxt(aSAr, Ho3.getClass());
   RObj = DTO_Ho3.getCtxtDTO();
   System.err.println("// __ |" + RObj.getClass() + "|" + RObj + "|");
// __
  }
}

// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~