Is there any mistake in this Java code?

Question

class Creature {    
   private int yearOfBirth=10;

   public void setYearOfBirth(int year) {
      yearOfBirth = year;
   }

   void setYearOfBirth(Creature other) { 
      yearOfBirth = other.yearOfBirth; // is this correct it compiles fine 
   }

   int getYearOfBirth() { 
      return yearOfBirth;
   } 

   public static void main(String args[])
   {
      Creature c = new Creature();
      c.setYearOfBirth(89);

      Creature d = new Creature();
      c.setYearOfBirth(d);

      System.out.println(c.yearOfBirth);
   }
}

Is there any mistake in this code?

Is "other.yearOfBirth" wrong? My faculty says it is wrong but it works fine for me.

Answer 1

As written, it will work, as you discovered. I suspect that there's a fundamental misunderstanding at play, though.

My psychic powers tell me that your instructor expected code more like the following:

class Creature {    
   private int yearOfBirth=10;

   public void setYearOfBirth(int year) {
      yearOfBirth = year;
   }

   public void setYearOfBirth(Creature other) { 
      yearOfBirth = other.yearOfBirth;
   }

   public int getYearOfBirth() { 
      return yearOfBirth;
   } 
}

class Program {
   public static void main(String args[]) {
      Creature c = new Creature();
      c.setYearOfBirth(89);

      Creature d = new Creature();
      c.setYearOfBirth(d);

      System.out.println(c.yearOfBirth); // This will not compile
   }
}

The misunderstanding is that you've only created one class-- your main application class. This effectively makes yearOfBirth a sort of hybrid global value that you can access from your main method. In more typical designs, Creature is a class that is completely independent of your main method. In that case, you must only access Creature through its public interface. You would not be able to access its private field directly.

---

(Note to any pedants out there: Yes, I know I'm simplifying.)

Answer 2

You have to ask your faculty to explain why they think it's wrong (its perhaps a question of style, or even a misunderstanding), so you can learn from it.

Ultimately this person is going to impact your grades. This is an excellent opportunity to have a positive interaction with them. The more involved your teachers are with teaching you personally, the better your opportunity for mastering your subject will be.

If on the other hand when you're told something is wrong you go away privately and ask the general internet community, there is a risk that you'll be told you're right and you'll end up a false sense of superiority over your teachers which will be very counterproductive.