Accessing private variable inside a library class

bontempos

I am trying to get an array from inside a library class, but the field is set as private :((

I used a java decompiler website to see this source of code:

public class MultiMarker
 extends NyARPsgBaseClass {
 protected PImageSensor _ss;
 protected NyARMarkerSystem _ms;
 public static final double DEFAULT_CF_THRESHOLD = 0.51;
 public static final int DEFAULT_LOST_DELAY = 10;
 public static final int THLESHOLD_AUTO = -1;
 private ArrayList<Integer> _id_map = new ArrayList();  //<<------- I WANT TO ACCESS THIS
 private final PMatrix3D _ps_projection = new PMatrix3D();
 private boolean _is_in_begin_end_session = false;

So this is what I had tried following some examples using Java as reference but still variable is NOT VISIBLE. maybe some casting problem...

import java.lang.reflect.*;
import jp.nyatla.nyar4psg.*;

MultiMarker nya;
void setup() {
  size(640,360);
  nya=new MultiMarker(this, 640, 360, "camera_para.dat", NyAR4PsgConfig.CONFIG_PSG);
  nya.addARMarker("patt.hiro", 80);//id=0
  nya.addARMarker("patt.kanji", 80);//id=1

  try {
      MultiMarker.class.getDeclaredField("_id_map").setAccessible(true);
      //or
      //Field idmap = MultiMarker.class.getDeclaredField("_id_map");
      //idmap.setAccessible(true);
      // ArrayList<Integer> castTest = idmap.get( ArrayList<Integer>() ); //--error
      // ArrayList<Integer> castTest = (ArrayList<Integer>)idmap.get(idmap); //--error

  }    
    catch (ReflectiveOperationException e) {
    throw new RuntimeException(e);
  }

  println(nya._id_map.size()); //field is not visible
}

GoToLoop

https://forum.Processing.org/two/discussion/9412/how-to-find-a-row-in-a-table
https://forum.Processing.org/two/discussions/tagged?Tag=setaccessible()

bontempos

Yes, so I have read these examples and tried to implement in the code above. I have read the reflect.class documentation and I believe maybe the problem is how I am trying to retrieve the ArrayList object using the Field.get( obj ).

But no. I have tried to access a private boolean variable using Field.getBoolean(obj) but I got "Can not set boolean field jp.nyatla......MultiMarker._is_in_begin_end_session to java.lang.reflect.Field" error

So it wasn't a casting problem as I expected...

GoToLoop

Gonna try to implement a more general approach and post it here when ready. :-h

bontempos

Thank you GoToLoop!! Got it working finally. Problem was using wrong object inside the Field.get method. #-o

import jp.nyatla.nyar4psg.*;
import java.lang.reflect.*;

MultiMarker nya;
ArrayList<Integer> idmapArray;

void setup() {
  size(640, 360);
  nya=new MultiMarker(this, 640, 360, "camera_para.dat", NyAR4PsgConfig.CONFIG_PSG);
  nya.addARMarker("patt.hiro", 80);//id=0
  nya.addARMarker("patt.kanji", 80);//id=1

  try {
    Field idmap = MultiMarker.class.getDeclaredField("_id_map");
    idmap.setAccessible(true);
    idmapArray = (ArrayList<Integer>)idmap.get(nya); //i was using generic obj here
  }    
  catch (ReflectiveOperationException e) {
    throw new RuntimeException(e);
  }
  println(idmapArray.size()); //print 2 OK!!
}

/*
public class MultiMarker
 extends NyARPsgBaseClass {
 protected PImageSensor _ss;
 protected NyARMarkerSystem _ms;
 public static final double DEFAULT_CF_THRESHOLD = 0.51;
 public static final int DEFAULT_LOST_DELAY = 10;
 public static final int THLESHOLD_AUTO = -1;
 private ArrayList<Integer> _id_map = new ArrayList();  //<<------- I WANT TO ACCESS THIS
 private final PMatrix3D _ps_projection = new PMatrix3D();
 private boolean _is_in_begin_end_session = false;
 */

GoToLoop

@bontempos, congratz for solving it alone. <:-P
Nonetheless, gonna leave the general solution here as reference for others: O:-)

/**
 * Get Private Field Example (v1.0.1)
 * GoToLoop (2016-May-23)
 *
 * forum.Processing.org/two/discussion/16771/
 * accessing-private-variable-inside-a-library-class
 */

import java.lang.reflect.Field;

void setup() {
  Table t = new Table();
  t.addRow();
  t.addRow();
  t.addRow();

  TableRow tr = t.getRow(1);
  Field f = getField(tr, "row");

  int r = (int) readField(f, tr);
  println(r); // 1

  writeField(f, tr, -2500);
  r = (int) readField(f, tr);
  println(r); // -2500

  exit();
}

static final Field getField(Object obj, String s) {
  return getField(obj.getClass(), s);
}

static final Field getField(Class<?> c, String s) {
  try {
    return c.getDeclaredField(s);
  }

  catch (NoSuchFieldException e) {
    System.err.println(e);
    return null;
  }
}

static final Object readField(Field f, Object obj) {
  f.setAccessible(true);

  try {
    return f.get(obj);
  }

  catch (IllegalAccessException e) {
    System.err.println(e);
    return null;
  }
}

static final void writeField(Field f, Object obj, Object val) {
  f.setAccessible(true);

  try {
    f.set(obj, val);
  }

  catch (IllegalAccessException e) {
    System.err.println(e);
  }
}