accessing private variables from a class within a class

package shop.data;

import VideoObj;
import shop.data.Record;

import java.util.Map;
import java.util.HashMap;
import java.util.Comparator;
import java.util.Collections;
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;

/**
* Implementation of Inventory interface.
* @see Data
*/
final class InventorySet implements Inventory {
 // Chose to use Map of Record, rather than RecordObj, because of
 // Java's broken generic types.  The story is too sad to retell, but
 // involves the fact that Iterable<? extends Record> is not a valid
 // type, and that Iterator<RecordObj> is not a subtype of
 // Iterator<Record>.
 //
 // Seems like the best approach for Java generics is to use the
 // external representation internally and downcast when necessary.
 private final Map<Video,Record> _data;

 InventorySet() {
   _data = new HashMap<Video,Record>();
 }

 public int size() {
   // TODO
   return _data.size();
 }

 public Record get(Video v) {
   // TODO
      Record r = _data.get(v);
          if (r == null)
              return null;
          return r;
 }

 public Iterator<Record> iterator() {
   return Collections.unmodifiableCollection(_data.values()).iterator();
 }

 public Iterator<Record> iterator(Comparator<Record> comparator) {
   // TODO
   return null;
 }

 /**
  * Add or remove copies of a video from the inventory.
  * If a video record is not already present (and change is
  * positive), a record is created.
  * If a record is already present, <code>numOwned</code> is
  * modified using <code>change</code>.
  * If <code>change</code> brings the number of copies to be zero,
  * the record is removed from the inventory.
  * @param video the video to be added.
  * @param change the number of copies to add (or remove if negative).
  * @throws IllegalArgumentException if video null, change is zero, if attempting to remove more copies than are owned, or if attempting to remove copies that are checked out.
  */
 void addNumOwned(Video video, int change) {
   // TODO
        if (video == null || change == 0)
              throw new IllegalArgumentException();
            
            Record r = _data.get(video);
            if (r == null && change < 1) {
              throw new IllegalArgumentException();
            } else if (r == null) {
              _data.put(video, new Record(video, change, 0, 0));
            } else if (r.numOwned+change < r.numOut) {
              throw new IllegalArgumentException();
            } else if (r.numOwned+change < 1) {
              _data.remove(video);
            } else {
              r.numOwned += change;
            }
          }
 

 /**
  * Check out a video.
  * @param video the video to be checked out.
  * @throws IllegalArgumentException if video has no record or numOut
  * equals numOwned.
  */
 void checkOut(Video video) {
   // TODO
        Record r = _data.get(video);
        if (r == null || r.numOut == r.numOwned)
          throw new IllegalArgumentException();
        r.numOut++;
        r.numRentals++;
      }
 
 
 /**
  * Check in a video.
  * @param video the video to be checked in.
  * @throws IllegalArgumentException if video has no record or numOut
  * non-positive.
  */
 void checkIn(Video video) {
   // TODO
      public void checkIn(VideoObj video) {
            Record r = _data.get(video);
            if (r == null || r.numOut == 0)
              throw new IllegalArgumentException();
            r.numOut--;
          }
 
 
 /**
  * Remove all records from the inventory.
  */
 void clear() {
   // TODO
        _data.clear();
      }

 public String toString() {
   StringBuilder buffer = new StringBuilder();
   buffer.append("Database:\n");
   for (Record r : _data.values()) {
     buffer.append("  ");
     buffer.append(r);
     buffer.append("\n");
   }
   return buffer.toString();
 }


 /**
  * Implementation of Record interface.
  *
  * <p>This is a utility class for Inventory.  Fields are mutable and
  * package-private.</p>
  *
  * <p><b>Class Invariant:</b> No two instances may reference the same Video.</p>
  *
  * @see Record
  */
 private static final class RecordObj implements Record {
   Video video; // the video
   int numOwned;   // copies owned
   int numOut;     // copies currently rented
   int numRentals; // total times video has been rented
   
   RecordObj(Video video, int numOwned, int numOut, int numRentals) {
     this.video = video;
     this.numOwned = numOwned;
     this.numOut = numOut;
     this.numRentals = numRentals;
   }
   public Video video() {
     return video;
   }
   public int numOwned() {
     return numOwned;
   }
   public int numOut() {
     return numOut;
   }
   public int numRentals() {
     return numRentals;
   }
   public String toString() {
     StringBuilder buffer = new StringBuilder();
     buffer.append(video);
     buffer.append(" [");
     buffer.append(numOwned);
     buffer.append(",");
     buffer.append(numOut);
     buffer.append(",");
     buffer.append(numRentals);
     buffer.append("]");
     return buffer.toString();
   }
 }
}

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package shop.data;

/**
* <p>Public view of an inventory record.</p>
*
* <p>Records are mutable, but cannot be changed outside the package.</p>
*
* <p>This interface should not be implemented outside the package.</p>
*
* <p><code>equals</code> and <code>hashCode</code> delegate to the
* underlying Video object.</p>
* @see Data
*/
public interface Record {
 /**
  * Returns the video.
  * <p><b>Invariant:</b> <code>video() != null</code>.</p>
  */
 public Video video();
 /**
  * Returns the number of copies of the video that are in the inventory.
  * <p><b>Invariant:</b> <code>numOwned() > 0</code>.</p>
  */
 public int numOwned();
 /**
  * Returns the number of copies of the video that are currently checked out.
  * <p><b>Invariant:</b> <code>numOut() <= numOwned()</code>.</p>
  */
 public int numOut();
 /**
  * Returns the total number of times this video has ever been checked out.
  * <p><b>Invariant:</b> <code>numRentals() >= numOut()</code>.</p>
  */
 public int numRentals();
 /**
  *  Return a string representation of the object in the following format:
  * <code>"video [numOwned,numOut,numRentals]"</code>.
  */
 public String toString();
}

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