Question

Having Node abstract class which Cell extends him .

In Cell I implemented public boolean equals(Node cmpCell) . I created Set<Node> closeList = new HashSet<Node>(); and when I execute closeList.contains((Cell) node) I debugged it and detect that it utterly ignores Cell equals I implemented . What I did wrong ?

Edit :

I changed in Cell to

@Override
public boolean equals(Object cmpCell)

and still closeList.contains((Cell) node) doesn’t using the above override .

2nd Edit :

In Cell class there is 2 members –

int colIndex ;
int rowIndex ;

the equals override just compare them to that both members of the 2nd class , I think it would be better I use HashMap<K, V> but still I would be glade to know how the hashCode should be looks like in such case ?

Answer 1

public boolean equals(Node cmpCell)

This is not a valid override. The syntax of equals method of Object class is: –

public boolean equals(Object)

And yes, as pointed out by @JonSkeet in comment, whenever you are overriding equals method, also remember to override hashCode method to follow the contract of equals and hashCode. Because if you don’t do that, then even if your equals method shows evaluates your instances as equal, the default hashCode implementation in Object class will generate different hashCodes for them, and hence they won’t be equal.

Also, ensure that, while calculating hashcode, you consider only those attributes, that you used to compare your instances in equals method. Else, again you will get incorrect result.

In addition to that, if you are using any IDE like Eclipse, it generates a very nicely overridden and compatible equals and hashCode method for you. You should be better using them.
You need to right-click on your class, go to source and select Generate equals and hashCode method.