読み取り専用オブジェクトの作成方法

public interface IReadOnly {
   public int getValue(int x, int y);
}

public class ReadWrite implements IReadOnly {
   private int[][] data = new int[4][4];

   public int getValue(int x, int y) {
      return data[y][x];
   }

   public IReadOnly getData() {
      IReadOnly iro = new IReadOnly() {
         public int getValue(int x,int y) {
             return data[y][x];
         }
      };
      return iro;
      //または return this;
   }

   public static void main(String[] args) {
      System.out.println((new ReadWrite()).getData().getValue(3,2));
   }
}

public interface ReadOnly {
  int getNum();
}

public interface ReadWrite {
  int getNum();
  void setNum(int n);
}

public class XXX implements ReadOnly, ReadWrite {
  private int num;

  public int getNum() {
    return num;
  }

  public void setNum(int n) {
    num = n;
  }
}

public class XYZ {
  private XXX source = new XXX();

  public ReadOnly getXXXAsReadOnly() {
     return source;
  }

  public ReadWrite getXXXAsReadWrite() {
     return source;
  }
}