Question

I have this simple class

public class Position{
   int x;
   int y;

   Position(int x,int y){...}

   public int hashCode(){
    Integer ix = this.x;
    Integer iy = this.y;
        
    return 13*iy.hashCode() + 43*ix.hashCode();
   }
}

Im storing instances in a hashMap, but then can’t retrieve them. I fear its the hashcode implementation. Is there any way to implement it when x and y are not Objects?

Answer 1

That you cannot retrieve them has nothing to do with your hashCode implementation.

As Integer#hashCode just returns its value, you could simplify it as

 public int hashCode(){
      return 13*iy+43*ix;
 }

Are you changing ix and iy after putting the object into the map? That is a big no-no and totally screws up the hashtable.

Also, you need to define Position#equals as well.